First thing to check is that you have the option to post into a future period, please see article about how to amend future period posting for a user.
If that is setup to allow you to post into a future period then our support team will need to investigate, run scripts or liaise with the hosting or development teams. Any Issues with contacting us, please see the following Get support in Dimensions.
Note: When entering Recurring Journals, you cannot change the period number in the Current Year box on the recurring journals entry screen, it picks up the date you put in for the first posting date. If you change the first posting date, this is the period it will be first posted in.