should I just delay one bit time in the ISR or set a timer to do it later
That depends
If you have spare hardware timer, absolutely use it, MUCH preferred.

If not, the you have two choices
a)Delay in the ISR ARGH, that makes the ISR timewise waaaay too long and other stuff may hiccup; However this (if you do not have a timer) is the only way you are ready to recieve immediately.
b) set a bit and delay in main this is second preference, but can get you in trouble if the other end start transmit too fast. However, if you have control of both ends use b) if a hardware timer is not available.

Erik