In Spring, if budding, I like to do it when the poncirus starts to "wake up". When it shows me growth then the bark starts slipping and you can bud. If cleft grafting or chip budding one can do it most anytime....as long as you do not have extreme temps. Spring and Fall are the times poncirus is most receptive.
Is it too late in the fall to do budding onto poncirus there? (Like marumi to poncirus) I'm mostly going to be trying Yuzu's, and Kumquats here. The record low was -10deg F in 1919. I want to try some cold weather hybrids, and perhaps try to graft them to speed up maturation. I have been collecting seedlings, hoping they could come back from the roots, if frozen to the ground.
No it is not too late where I am. If in fall you have temps that are conducive to grafting, (70 to 80) go ahead and do it. Even budding can be done. Dependant upon weather you might want to wait until Spring to force budded stock.