First few hours of lights out temp advice plz...

Looking for a bit of advise on night temps please guys. Im in the attic and run my lights on at night. My lights on temps and humidity are spot on. My issue is immediately after the lights go out my temps are dropping to around 13c-15c (55f-59f) , humidity (50-60%) . The temperature then gradually rises over around a 3 hour period to 17c-20c (62f-68f) where they stay like that until the lights come back on.

Is this likely to cause issues ie stunted growth or delay nute uptake as its only for the first few hours? Im thinking of getting some tube heaters to come on for the first 3 hours to increase it slightly but due to lack of funds atm i thought id ask here for some advice first before going and wasting cash on something that might not work

The space im working with is about 1.5m2 and i was looking at a couple of 80w tube heaters , is this likely to be sufficient for the space ? The strains im working with are indica dominant (critical kush & critical fem)

Any advice appreciated

I think in general you want to stay above 16c, with about a 10* variation from lights on/off.

so do you think 2 80w tube heaters would do the trick?

Can you get a good fan speed controller with night and day temp control?
Would probably cost more but in the long run save you money if your not having to run heaters and running fan at reduced speed.
The environment would be much more stable that way.

** Just an update , a decent fan controller is out of my budget at the minute

Bought a 700w oil radiator and run my intake from another room , night temps now 18-23c , rh 40-50%

thanks guys