TEMP drop night?????????? help

Ok as my setup is moving on with the 4 x1000
i want to know do i have to let the TEMP drop when lights are off or leave it all the time more or less around 24 deg cel because winter outside goes down -15 .....

Some temp drop in dark time is actually good but I keep it to 5 degrees and I'm on F degrees.

-15c is pretty low but not sure what it is in F. When the temp goes below 40deg f. I bring them in.
Do some conversions to f.

I keep my room at 75-78 during the day, after lights out I drop it to 70-73.
when temp goes below 35-40 its not good.

Yea a 5 degree drop is good.

Dont want it to get much over the low 80s in the day though

A slight 5-10 degree F drop or rise in temps between 'day' and 'night' cycles is a good thing, and is referred to as 'dif'. A little dif is good, and can do neat things like bring color hues out on plants that normally would have remained green without the dif.

One should strive for about 72 degrees F at night and 76-78 degrees F during day. A reverse dif (warmer at night, colder at dark) is a bad thing, and can make plants stretch unnecessarily and do other weird things. So as long as your dif is negative at night, and not dropping too much overall then it is beneficial.

If temp changes are greater then 15 is that too much. if so will it just slow growth or change potency?

Temps below 68 degrees F slow growth, and at around 55 degrees F growth basically stops. Ambient air temp may be lower if the substrate and rootmass temp is kept within the acceptable range.

After about 85 degrees growth is slowed as well, and as temps rise above 85 plants will stretch and growth becomes more loose and buds become more 'airy'. The addition of CO2 allows one to run higher temps without being detrimental to the plants, but even at 1600 ppm you can only go so far before high temps become an issue again.

dc