Global minimum sync time for mirrors
@tiagonbotelho is/was working on a feature that lets you set custom sync times for mirrors, on a per project basis. For GitLab.com we want to enforce a sensible minimum for all projects. For example, we want to set the minimum to either 12 or 24 hours. As a result, when determining the sync time the code has to check this minimum value. If the project's sync time is lower it will use the minimum instead.