For me it's probably 15 minutes or so for 3 tubes. Easy enough and I can remember maybe 1 of my patches ever failing. Of the number of tubes that I've patched (it's a big number) I think my probability of failure isn't far off new tubes right out of the box. I've ridden tubes with 5+ tubes before without a thought. I don't even keep track of them, and only really toss them out when there's a stem or other catastrophic failure that can't be repaired.

It's only ever noticeable when on the trainer where you can feel the bumps as the patches roll over the barrel. Aside from that there's no difference at all in using patched tubes, assuming they've been patched correctly.

-Jeremy