Very few if any reports so far of folks needing to recap PCI based Macintoshes. And Beige G3 is a generation later than that.
On the other hand, the first Mac I needed to recap was a IIci and that was in 1995, only a few years after manufacture.
So, it can take 2 years or 20 years. It seems to vary a great deal with the machine, probably the caps origianlly used, and probably the conditions under which it was stored.
I'd say, you should not expect to need to recap it. If you have mysterious problems with it, you may want to try washing/cleaning the board. If that clears up the problems, then it probably needs a recap.