You can add a reminder to a note: Dates, Events, and Reminders
Also alarms are in a way just a variation of reminders as you can for example create a reminder by typing \remind(in 30 minutes)
Timers that count up are much rarely used in note-taking I’d argue, for those the alternative would be to add a timestamp, for example by typing \date or \now.
See also Text Actions Cheat Sheet