In most cases, there is no specified time period required to activate an eSIM. Your users can activate the eSIM at any time as long as there have not been any network provider changes or network blocking. If these changes take place, they will be communicated to the you via email.
Please note that some eSIMs do required activation within a specific time — generally within 90 days of purchase. This is a newer requirement from network providers due to regulations surrounding MSISDN usage.
Additionally, some eSIMs activate at the time of installation, such as the dtac eSIM for Thailand.