I would like to be able to save and recall up to, say, 5 different time selections in a project. (Please let me know gently if I have missed this or it's in an extension or something)

It's indeed in the SWS extensions, 5 slots available. type "save time" and "restore time" in the actions search filter. (SWS extensions must be installed, of course)

wow, this is awesome. thanks for the hint, nofish. and thanks again to sws!