Clarification please.....

Please forgive my trivial question but I have never flown Virgin before.
I now know that I can request seats at 90 days.
I recently read on the forum that because a passenger had not done online check, I think they managed to do so a few hours before departure their preferred seats had been reallocated. How early/late can you do online check in, hoping to keep requested seats?
Flight will be LAX-LHR[Arriving in LA on a cruise]
Thank you in advance
Susan
I now know that I can request seats at 90 days.
I recently read on the forum that because a passenger had not done online check, I think they managed to do so a few hours before departure their preferred seats had been reallocated. How early/late can you do online check in, hoping to keep requested seats?
Flight will be LAX-LHR[Arriving in LA on a cruise]
Thank you in advance
Susan