Recirculating DWC doesn't really have a current with the small hoses usually used, but it's generally recommended to get full cycle at least every 4 hours. That's about what alot of rdwc systems I've seen claim as well. It's enough to keep ph and ec balanced between buckets, but not optimal for performance.
Undercurrent is different, alot of guys are getting their entire volume (sometimes 50+gal) cycled every few minutes, using pumps instead of passive flow and 3"pvc instead of 1/2" tubing. But that also brings other benefits with it (ease/speed of maintenance, aeration, lower ec requirements, etc). So for once, more is better.