New bun advice!

When you get a new bun how long do you leave it before not worrying about it passing on anything to your other bun?? I have my buns at different ends of the garden and they have there own things, when I have the new one spayed I hope to bond them can they be near each other in runs before that??

I keep foster buns away from my others for two weeks, after which I let them come along side mine in the run.