When is long enough

what is considered an exceptable time limit for leaving primary CR123's in your lights while sitting on a shelf waiting to be used? would that time limit also hold true to RCR's?

Welcome! Just to give you a heads up, the moderators will probably move this to the Flashlight Electronics forum.
CR123 are lithiums so they have quite a long shelf life. I think after 10 years they still have 85% of their capacity. They are also more tolerant of extremes of temperature. They should be OK to sit in a light for quite a while. If you have a multi cell light it is important that the voltage of the cells match otherwise you can run into problems like venting with flame. If you do not have a volt meter and if if you have a multi cell light I think it would be a good idea to store the light without batteries in them. Single cell lights are fine though. With regrad to RCR123's they can retain their charge for quite a while, I think I read up to a year. For the health of the cell it is better to store them at around 40% if they are not going to be used for a while. I think the safest thing to do is store CR123 batteries by themselves and use the RCR123's for day to day use.

Well,Primary Batteries have a 10 year shelf life.

I would be sure to test the batteries every 6 months or so.

Otherwise: <10