Summer is a busy time for people who love and grow a lot of sub-tropical and tropical bonsai. I live in Southeast Texas, and start to repot, defoliate and wire my ficus in June. By this time the Texas heat is intense, daily temperature is in the 90s with heat index over 100ºF; it is very hot working outside even under the shade. I repot my ficus later than what most people living in Zone 9 would do because I want my trees to take advantage of spring growth spurt before doing any major maintenance work. You may have read advises such as repot tropical trees when the night temperature is above 60ºF. That is correct for safety reason but it does not mean you have to plunge right into it when the weather warms up. Just take it easy and let your tree grow, let them become healthy and strong before repotting and defoliation.
Our last frost date is around third week of March. In early April I moved my ficus out of the greenhouse and let them sit under full sun in open air. Ficus grows virtually year round for us, when over wintering in greenhouse they just slowed down their growth, hardly noticeable but definitely continue to grow. That’s why I do not remove my fertilizer in winter. Once outside, with plenty of sunshine, fertilizer and water, there is a sudden surge in new growths. I let them have about 2 months of growth to gain vigors before starting any work.