lighting question

Ok so i am 4 weeks into flowering and the issue i have, is that i could do with the lights been on at night but at the minuet they are on from 9 in morn till 9 at night.

The rason for this is tempratures are droppoing too low on a night, so the idea is lights keep em warm on a night and the central heating keeps em warm in day.

What would be the best way to sort this with out stressing the plants? would you leave the light on or off for 24 hours to get it to the right time?

Merry Christmas to all my RUI family.

4 weeks into flower 24 hour dark period is preferred compared to a 24 hour light period.