Timer Fields
A Timer runs a list of actions after a delay, either once or over and over. Like a Multi-Action it has no appearance - the user never sees it - and like a Multi-Action it is where a form does something without anybody clicking anything.
Typical uses: run something a moment after the form opens, once everything has loaded; refresh a search or a set of required documents every so often on a screen left open all day; step a display along on its own.
Settings
Field Name - The name used to refer to the timer in conditions and in actions.
Number of Seconds - How long to wait before the actions run. Decimals are allowed for a fraction of a second. Set it to 0 to run as soon as the form loads, and leave it empty to disable the timer entirely. {field} notation can be used, so the delay can come from a field on the form.
Run Action Repeatedly - Turn this on for a timer that keeps going. Turn it off and the actions run once.
Seconds Between Actions - How long to wait between runs when the timer repeats. Decimals are allowed. Leave it empty, or at zero or less, to stop it repeating. {field} notation can be used here too.
Run When - A condition that decides whether the timer runs at all, built the same way as the conditions described in Field Conditions. Use it to keep a repeating timer from running where it is not wanted - only on the record screen, only for internal users, only while the record is at a particular workflow step.
Actions - The list of actions to run, in order, each with its own Execute When condition.
Points to watch
A repeating timer keeps running for as long as the form is open. Anything it does that reaches the server - a search refresh, a REST call, an Action Set - happens once per cycle, for every person with the form open. Set the interval to the slowest that is still useful; a few seconds is rarely necessary where a minute would do.
For a one-off action as the form opens, a Timer set to 0 seconds is the usual way to have something run after everything has loaded, which a form-load action cannot always guarantee.
Where the timer's work is more than a step or two, put the sequence in a Multi-Action field and have the timer trigger that. The sequence is then easier to test - a button can run it on demand - and can be reused elsewhere.