How often - depends on the project and the development process, how to roll out the update and make changes.
Time - when the server load is minimal.
Jeff28 answered on July 9th 19 at 13:18
There are no regulations. It all depends on the requirements of the service.
That is, the main requirements are:
1) to minimize a simple service, ideally so that users do not notice downtime, or they were not critical.
2) to minimize the risks of making changes (put tested changes, have a ready and thought-out roll-back plan in case of a rollback)
3) to reduce the cost of making changes. For example, if it can be done in business hours, will not have to pay overtime.