This article explains how new export quotas (10, 50, 100 or 200 depending on the contract) are made available on a daily basis.
Once you have performed an export, you cannot use the request again for 24 hours. The number of possible requests is not reset at a specific time, but is recharged over time (24 hours).
Example:
You have a Premium Standard licence with a maximum of 10 export requests per day. If you make a request at 12.32pm, it will not be available until 12.32pm the following day. This leaves you with 9 out of 10 possible requests that are recharged in the same time interval.
Please note:
To ensure that requests work properly regardless of time zones, they are handled according to this scheme.