Can I use outdoor timer indoors.Its a dusk to dawn timer but no lights will be on

Yes. Must keep switch turned ON.
Outdoor lights will only come on when motion is detected, otherwise light bulb does not come on. So the indoor wall switch does not work as override since the motion sensor takes over as the sole switch.
Copy following link for wiring illustrations:
http://waterheatertimer.org/How-to-wire-occupancy-switch.html#motion
Other solutions include adding separate motion sensor light nearby and keep porch light so you can turn on-off when desired.
Another option is to add photocell to outdoor light so it turns on automatically at dusk.
Another option is to use outdoor yard timer with dawn-dusk capability:
http://waterheatertimer.org/Woods-timers-and-manuals.html#outdoor
Another option is to replace indoor wall switch with with dawn-dusk timer, that can also be used as ordinary on-off switch so you can turn porch light on-off when desired. Timer such as Intermatic ST01C offers simple 2-wire connection.:
http://waterheatertimer.org/ST01C-program.html
Gene
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Woods 83660 security timer appears to be same/similar as Coleman 2001/Woods 49647
Instructions: Timer turns ON automatically at dusk
Use dial to set 4 possible options:
Off = always OFF; ON - always ON
Dusk-Dawn = ON at dusk, OFF at dawn
2,4,6,8 hours = ON at dusk, lights OFF 2,4,6,8 hours later
Woods Model 2001-49647 manual

7120Z timer is electro-mechanical astronomic dawn-dusk timer so it should perform fine on gfci breaker.
http://waterheatertimer.org/Tork-timer-and-manuals.html#7200

The purpose of gfci is to identify electrical short at the moment it happens and trip off so nobody gets shocked.
Typically you find gfci with outdoor wiring, and astronomic timer controls outdoor lights.
If you locate box outdoors, it must have NENA3R raintight indoor/outdoor case.
If timer is indoors, then NENA1 enclosure/case is fine.

I see nothing in the manual that says 'outdoor use only' EXCEPT timer runs on photoelectric eye.
Timer turns ON automatically at dusk, so if timer is inside, and indoor lights are ON, then timer stays OFF.

http://www.intermatic.com/~/media/files/intermatic/products/instructions/timers/hb51rc%20-%20english.ashx

http://www.intermatic.com/products/timers/consumer%20outdoor%20timers/electromechanical%20timers/hb51rc.aspx


To use timer outdoors.
Plug timer into wall.
Timer turns ON automaically at Dusk.
Rotate dial to set how long timer will stay ON.
Set timer to turn OFF 2 4 6 8 Hours after dusk
Set timer to turn off at dawn
Set timer to ON so lights are ON full time
Set timer to OFF so lights are off full time.

Here is how it works. The push button repeats itself in following sequence (must plug in).
F 1 2 3 4 5 6 7 8 9 A d 1. 2. 3. 4. 5. 6. 7. 8. 9.

F: timer is off.
1 2 3 4 5 6 7 8 9: from dusk to dawn count down number of hours repeated every day. That's most useful to control outdoor lightings.
A: from dusk to dawn count down number of hours which is randomly selected by this timer. Which is usually for indoor use to turn lights on and off for number of hours. The randomly selected hours is a security feature so that lights on (on from dust, but off randomly) time shows no pattern to outsiders.
d: just on from dusk and off at dawn. It is also used to control outside lights but just a little wasteful in my opinion.
1. 2. 3. 4. 5. 6. 7. 8. 9.: meaning count down number of hours starts from the time when the button is pushed so that you can have a countdown timer at any time.

That sounds like the Woods 17321 Dusk-to-Dawn yard stake
Product image:
http://www.amazon.com/Woods-17321-Outdoor-3-Outlets-6-Foot/dp/B000BHN4H8

Manual
http://waterheatertimer.org/pdf/Woods-17321.pdf

If this is not your timer, check following page:
http://waterheatertimer.org/Woods-timers-and-manuals.html

Instructions:
Yard stake control outlets, and turns ON automatically at Dusk
Rotate dial to set options:
Rotate to OFF > outlets OFF
Rotate to ON > outlets ON
Rotate to Dusk-dawn > outlets on at dusk and off at dawn
Rotate to 2 4 6 8 > outlets on at dusk and off 2 4 6 8 hours later

Woods makes several outdoor timers:
http://waterheatertimer.org/Woods-timers-and-manuals.html

Image that shows with this post is Woods model #49647.
Below are instructions for #49647 timer.

If your timer is different, add a comment with model number and I'll post instructions for that timer.

Woods model #49647 is outdoor timer with photoelectric control that turns timer ON at dusk.
There are 4 possible settings that show on dial.
Rotate dial to make timer selection.
OFF = timer is OFF full-time until you change dial.
ON = timer is ON full-time until you change dial.
Dusk-Dawn = timer turns ON at dusk and OFF at dawn
2, 4, 6, 8 hours = timer turns ON at dusk, and turns OFF 2, 4, 6, or 8 hours later.

Here is how it works. The push button repeats itself in following sequence (must plug in). F 1 2 3 4 5 6 7 8 9 A d 1. 2. 3. 4. 5. 6. 7. 8. 9.
F: timer is off. 1 2 3 4 5 6 7 8 9: from dusk to dawn count down number of hours repeated every day. That's most useful to control outdoor lightings. A: from dusk to dawn count down number of hours which is randomly selected by this timer. Which is usually for indoor use to turn lights on and off for number of hours. The randomly selected hours is a security feature so that lights on (I believe the on time is within the range of 1 hour from dusk set by the timer) and off (it is randomly set, you can see the display blinking showing the selected countdown hours) shows no pattern to outsiders. d: just on from dusk and off at dawn. It is also used to control outside lights but just a little wasteful in my opinion. 1. 2. 3. 4. 5. 6. 7. 8. 9.: meaning count down number of hours starts from the time when the button is pushed so that you can have a countdown timer at any time.

Here is how it works. The push button repeats itself in following sequence (must plug in).
F 1 2 3 4 5 6 7 8 9 A d 1. 2. 3. 4. 5. 6. 7. 8. 9.

F: timer is off.
1 2 3 4 5 6 7 8 9: from dusk to dawn count down number of hours repeated every day. That's most useful to control outdoor lightings.
A: from dusk to dawn count down number of hours which is randomly selected by this timer. Which is usually for indoor use to turn lights on and off for number of hours. The randomly selected hours is a security feature so that lights on (on from dust, but off randomly) time shows no pattern to outsiders.
d: just on from dusk and off at dawn. It is also used to control outside lights but just a little wasteful in my opinion.
1. 2. 3. 4. 5. 6. 7. 8. 9.: meaning count down number of hours starts from the time when the button is pushed so that you can have a countdown timer at any time.