Hi,
As general rule develop it ASAP but this is not always practical if you are away on holiday or otherwise engaged. The danger is in leaving it in the camera, or it its casstte after removing it from the camera, and leaving it to hang around for a while in high temp comditions - like the boot of your car! If you have to put off developing a used film better to store the film in a fridge until you have time to do the develpment. The problem occures when you haven't used all the film up and it stays in the camera until you next go out to shoot I/R which could be weeks / months away. This happens to me from time to time and I take the precaution of storing the I/R loaded body away from sources of heat that it may get exposed to for a long time. I have been practising this for about 20 years now and have had part used I/R film in my camera for a number of months and have had no problems with degrading the image at all. No need to worry too much about this - just go out and enjoy your I/R work but be a bit careful where you store the camear / film cassette afterwards - especially if you are shooting with Kodak I/R film.
Cheers,
Neil.