Lennox furnace 17 yeanrs old. flame comes on and the shuts down sometimes right away some times in a few minutes. We have the furnace go down to 58 at night. It takes all day to get back to 67.

I have a Lennox G40UH furnace. The burners fail to ignite about every 5th time. The furnace will try to ignite the burners then shut down. Once in a while the temp will drop down to 62 then fire up. I have only gotten a Diagnostic code once "Watchguard - burners fail to ignite" once I shut the power down and it started.
The furnace is clean, 5 years old, the flue is not clogged.

Sounds like a dirty flame sensor.
Also 9 degrees is a large swing to recover. Most specialist will advise no more than a 5 degree set back, otherwise recovery time eliminates any savings you may achieve.