If you've broken up before it might take less time to get talking again since its happened before, however I would suggest a couple on months not talking or meeting up, just to get over each other and move on.
Me and my ex tried to be mates after breaking up but I still had feelings for him and he got angry and stressed at me, plus we still slept together, which was worst mistake ever! and now he's cut me out of his life and won't say 2 words to me even on msn.
So deffo leave it a while and as for being f*** buddies, its up to you but if one of you gets anothe bf or gf it could get messy
Good luck though x