No, but as I understand it, the OP is asking for when, precisely, it is no longer possible to cancel and claim a refund.

They are clearly not talking about the usual position whereby a person can cancel months, weeks or even days before departure without worry.

I do not know when, exactly, it becomes impossible to cancel "in time". Is it when OLCI closes? Is it when the airport check-in closes? Is it when the gate agent closes the flight? Is it when the gate agent hands the manifest to the captain? Is it when the aircraft door closes? Is it at pushback? Is it when the craft reaches the active runway? Is it at wheels up?

I'm pretty sure that for most, if not all, of these timepoints, it would not be possible to simply cancel the ticket online or in the app, and whether and if you can get through to an agent on the phone who has the authority/ability to cancel the ticket at any of these times is also a bit of a worry.

My advice to the OP is not to plan a course of action where they literally will not know whether/if they want to cancel a flight until so close to departure.

"Before departure" is not a precise statement; you cannot derive from this at which specific moment in time cancellation may become impossible.