It might vary from one instructor to another but for the snorkel swim we had to stay on the surface and couldn't use our hands. I kept my BC deflated and my hands clasped together and placed on my butt to help keep my fins under. I was using my heavy jetfins that have served me so well.
The 25m isn't really that hard, we make our OW students do it at the beginning of the course just to get an idea of their underwater swimming ability. At the end of the quarter they do it again but are allowed to wear all their snorkeling gear, I think the record for a single breath swim in our program is roughly 60m with snorkel gear. The trick is to take 3 deep breaths, hold the fourth breath then swim as close to the bottom as you can. We suggest watching 1 row of tiles. When you feel the urge to breathe exhale just a little and keep following your row of tiles. When you feel the urge to breathe again look up, you should be near the end of the pool, exhale slowly and kick for all you're worth.
Ber
The 25m isn't really that hard, we make our OW students do it at the beginning of the course just to get an idea of their underwater swimming ability. At the end of the quarter they do it again but are allowed to wear all their snorkeling gear, I think the record for a single breath swim in our program is roughly 60m with snorkel gear. The trick is to take 3 deep breaths, hold the fourth breath then swim as close to the bottom as you can. We suggest watching 1 row of tiles. When you feel the urge to breathe exhale just a little and keep following your row of tiles. When you feel the urge to breathe again look up, you should be near the end of the pool, exhale slowly and kick for all you're worth.
Ber