You said you haven't got any fruits in your grow but that La Diva is a sweet blueberry and one of my favourites. I am sure you are going to enjoy it!
The best temps for your plants are between 20 - 26c for germination and growing. once the plants are growing the optimum temp is around 26c with lights on and 20 with lights off.
if you get over 30c without co2 enrichment you can cause stunting, I stunted a whole lot of plants in the past by having my temps too high.
I use a guide of 18c to 30c as the safe zone anywhere outside of these temps I know I need to take immediate action to correct it.