It's probably a default setting, not solely related to RBP, and I think it's less than 60 seconds.

Sometimes when I'm organizing Dos I'll write a PM w/ details, then cut/paste it to send to individual FTers. Since cutting/pasting only takes a second or two, in addition to clicking on send new message, typing in a handle, it's a short period of time before I'm sending the next PM. But I'll get a message saying I need to wait (20, 4, 1, fill in the blank) before sending another PM.

Did it occur to you that the reason for the delay in RBP is to also prevent someone using that like a spammer would - ie, doing RBP in a rapid fashion?

Cheers.