They do grow all year long, but slow down substantially in the winter due to low light, short days, and usually cooler temperatures. Once past the vernal equinox, their growth rate picks up and peaks in Jun, Jul, Aug. Any serious work, like heavy pruning and repotting/root-pruning would best be done in June. Father's Day or the summer solstice are easy to remember and serve as excellent target dates for operations that cause anything other than minor stress.

If you're interested in knowing more about the plant you can look over this thread about Ficus benjamina (weeping fig). The cultural preferences of Ficus b are virtually the same as Ficus lyrata/ FLF.

Good luck!

Al