How Important Is It to Train Outside in the Heat of the Day

How important is it throughout your training program that you're doing sessions in the heat of the day. How do you expect your body to be able to race at the same output if you're training for something completely different again or the conditions are very different? You need to consider the months if if you're raising altitude you go of course altitude to acclimatize so that you can't actually output according to the demand altitude you don’t prepare at sea level like way with heat you have to prepare for the heat in. If the race is during the day you have to prepared for that and if it's cold conditions you can't expect to perform very well even in very cold conditions