You can require it, but there isn't a way to automate anything around the requirement. In other words, if someone doesn't sign a document by a specific date or time, what you do is a matter of company policy.
Here are a few options that come to mind or that we have seen others use to encourage timely signatures:
Reminder Email: Hover over the document in the Documents Tab and click the Remind button to send a manual reminder email.
Double-check Email: Hover over the document in the Documents Tab and click the edit icon to double-check that the email used for the signature is correct. If it's not, update the email and resend.
Consequences: A more dramatic approach is to spell out the consequences of not signing the Document by a specific date in an email or text communication - E.g., your reserved spot will be released, and non-refundable payments will be forfeited.