With a San Diego Webmaster Services Monthly plan, will unused hours carry over from month to month?

No, unused hours do not carry over, however, you may use your hours for more than just site updates. If you find that you have not used all of your hours for a month, you can request offsite backups, Joomla upgrades, Extension updates, a site review and/or clean-up, content review, or consultation. There’s always work that can be done!