Is it common for freelancers to have a minimum number of hours they will bill? If so what is the minimum number of hours?
I bill hourly in 1/2 hour increments, but I have not set a minimum number of hours. The issue is I get many small support projects/requests (for example lets 5 requests, that take about 20-30 minutes each) on a weekly basis that usually interrupt my work on a long term projects (lets say 1-2 week project). I may only work on the small project for 20-30 minutes, but the loss of effort/productiveness on the long term project is greater than that. The interruption breaks my flow from getting things done on the long term project. So I'm thinking a 1 hour minimum or maybe a 1.5 hour minimum is not too much to ask. Or is there some other common practice to cover the loss in productivity caused by small support projects/requests.
If it help here's a little background. I'm a freelance web developer, and have been working for myself for 10 years. Most of the requests are to support sites I've built. Many requests are for software upgrades. Some requests are just to add content. Some request are for site enhancements (install, configure, and/or stylize a plugin).