I have asked friends to come in and take care of the bunnies overnight a couple of times, and it worked out fine. When you say you feed him twice a day, do you mean veggies, pellets or hay? The reason I ask is that hay should always be available, so I really pack the hay rack full and leave a basket or two of additional hay in the pen, as well as an additional water bowl just in case. My guys usually get greens twice a day, but when people are stopping in for an overnight I only ask them to feed greens once. To save work, you can premeasure the pellets, and keep a regular bunny salad wrapped and prepared in the fridge, so all your friends have to do is top off the hay rack and water bowls, give the prepared meals and go on their way. You can prepare a small note with what to feed and how, with a contact number on it just in case.
For more than an overnight, I always go with a sitter. Too much bad stuff can happen to a rabbit in 48 hours to leave them unattended for that long.