They will be fine, anything up to 35 degrees is do-able, they will just drink more.
You could shift your timer so the dark period is during the hottest part of the day i.e. 11am until 5pm, thereby running your lights mainly during the night and cooler parts of the day - morning and evening.
At this age, just give them an extra long day to move their "lights on" time, rather than giving them an extra long night, - that is if you intend to alter the timing of the light cycle.
Hope this helps, Organoman.