Background information:
zo_callLater is nothing else than an
EVENT_MANAGER:RegisterForUpdate
with a pre-defined identifier prefix "CallLaterFunction" and an attached suffix which is not pre-defined.
https://github.com/esoui/esoui/blob/...alapi.lua#L197
And either zo_callLater or EVENET_MANAGER:RegisterForUpdate both return the unique ID of the registered handler so you can use this one to unregister it again via EVENT_MANAGER:UnregisterForUpdate