The client you're playing on determines the buffering. If you're on a PC, you can set the buffer from 3 seconds to 20 (I think).
As for your issue, it's try you could be having issues with radio interference. But the issue could be on the PC where recording is located to anywhere in between. If you're using Media Center, it tends to be a more more nick picky about your network setup. I have found I get better performance by using workgroups and setting up my DVR libraries through it. You can use the shared drive, but MC doesn't play as nice; plus, you can't delete content except on the host machine that recorded it. Also, don't forget to check for driver updates for your NICs or firmware updates on your router.
Although Plex can play WTV files, it's not the best solution. FF or RW don't work well. Skip F or R works ok on the PC client. And the mobile and Roku, I find it Plex craps out. So, you'll have to endure commercials. I have used it here on there like when I'm on vacation away from home to catch up on TV shows or something.