Gjac, yes, only to the first. At the time we didn't know much about the second wave or how to get there or how long it would take.
I asked my husband if he could remember how long it took us to hike in. He wasn't sure but thought maybe 2 hours. However - we stop, a lot, to take photographs. We missed the turn-off to The Wave and continued down the wash on the Buckskin Gulch Trail for a good distance before we realized our mistake. Easily lost 30 minutes, maybe more, on having to backtrack. May 18 was hot. We hit the high 90s and so we stopped a lot to drink. This was also our first hike over slick rock and through areas with no real established trail. After the Ranger told us a lot of people never find The Wave, we spent probably more time than necessary checking the map, landmarks, compass, and GPS.
It took us less time to hike back out than it did to hike in. We were more confident of the trail, especially since we had our GPS cookie crumbs to follow. We'd also already photographed most of the "cool stuff" on the way in so didn't stop as much.
In all from start to finish at the trailhead, we were gone between 5 and 5 1/2 hours.
If you can't get a permit for The Wave. Or if you decide your knees might not co-operate, there is another hike we did on another trip. It's to a formation called the Nautilus. Compared to The Wave, it's tiny and not nearly as spectacular, but the hike isn't as long or hard. The formation is mostly white with a few scattered bands of golden oranges and yellows scattered through it. A Ranger told us about it and we considered it worth the effort. However, we are a bit nuts about rock formations and interesting geology so others might not agree.
Whatever you decide to do. Enjoy. It's so beautiful out there.