As you may know, for my PERSONAL practice I use my local climate/watershed/landmass for my cues. So it's still a few weeks from Imbolc for my personal practice.
However, last night I celebrated Imbolc with my coven. Because we set dates for celebrating High Days all at one time, once a year, so we are better able to arrange everyone's schedule. And because the group members are spread over such a large geographical area that, say, hawthorn leaves are the size of a squirrel's ear at vastly different dates for some of us.
If we were all in the same neighborhood, rather than spread across 3 states, we might better be able to see the local signs and then celebrate as a group 3 days later. But that's not our reality. And even with everyone knowing the date in advance - had the celebration been on a night the Spawn was called in to work I'd not have been able to make it, and one coven member had to miss the ritual as it was.