In general it takes 6 weeks for bone to heal - this includes fusion with autograft bone however I assume the fusion was done with a screw.
You should discuss return to activity time frame with your orthopedist because he or she alone knows the details of the fusion i.e. the extent of the initial damage, how the operation went, what was the quality of bone, and which specific bones were fused - talus to the calcaneus and/or talus to the navicular.
Remember that strengthening muscles around the ankle and in the foot will take 6 weeks plus 3 weeks of proprioceptive training. So total recovery time takes about 4 months minimum.
When you do return to regular activities, do so gradually. Problems may not present themselves for several days or weeks. So easy does it.
Let us know how it goes.
Tom Plamondon PA-C, PT