Hello Martin! I think that it's a very interesting area and it's worthy to go: Semuc Champey is cool, a great activity for half a day. If you only do this, you need a day in the area (a night and a day). I recommemd to go to Semuc Champey early, so this way you avoid the hords of people coming up from Coban in a day trip (you could also do that, but you'll arrive late and won't enjoy the pools that much). What else you can do? You can visit the Lanquin Caves (with many many bats) and then do some rafting (depending on the season). My advice would be to spend a night there and after Semuc Champey head up to Cobán. I wouldn't give it much more time. Anyway, the pools are gorgeous so I wouldn't think twice about going there! Enjoy your trip!