[plt-scheme] Can I create an event that's like an alarm, but can be reset?

Here's what I'd like: an event that I create just like an alarm (i.e.,
by calling, say (define a (resettable-alarm-evt 1234))).  It acts just
like an alarm, _except_ if, before it is ready, I call (reset-alarm!
a), then it will now be another 1234 milliseconds before it goes off
(assuming I don't reset it yet again).

Is there some way I can create such a thing?  Or perhaps I can use an
existing synchronizeable event, but to be blunt the docs for events
make my eyes glaze over -- I don't understand what half of the event
types are for.
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