Time involved? I don't know about Pro-Seal, it would depend upon the actual steps used in the process. But I'm gluing my RV-3B fuselage together before riveting it, using a structural glue, and I can tell you that it adds a huge amount of time to the construction.
If the Pro-Sealing was done neatly and the riveted joints look even and smooth, you've probably got an exceptionally well-built airframe. If you ever need to repair something, though, I left a tank sealant removal thread in the Tips section that could come in handy.
Back in the BD-5 days, that airplane was built using Pro-Sealed joints and low-strength blind rivets. The word was that the sealant improved fatigue life of the riveted joints. That specific type of rivet, Avex, is not used on RVs.
Oh - why am I using glue? Two reasons. First, it acts as an assembly aid much like clecos except with zero shifting or moving. Second, if done right (which is something I'm still working on), it can result in an exceptionally fair and smooth skin.
Dave