Possibly mark payment for next month in office appointment

• Write a check for later
• Assign to a later time
• Follow in time
• Put 12/31/2020 on checks, say
• Indicate a later time, as on a check
• Be subsequent to
• Prepare for later, in a way

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Postdate \Post"date`\, v. t. [imp. & p. p. Postdated ; p. pr. & vb. n. Postdating .] [Pref. post- + date.] To date after the real time; as, to postdate a contract, that is, to date it later than the time when it was in fact made. To affix a date to after ...

Wiktionary Word definitions in Wiktionary
(context obsolete English) postdated; made or done after the date assigned. v 1 (context transitive English) To occur after an event or time; to exist later on in time 2 (context transitive English) To assign an effective date to a document or action later ...