Practicing alone? That’s a pretty personal choice.
Because I practice with a coven, I’m usually in for a ritual for all of the greater Sabbats, and at least a feast/party for the lesser Sabbats, unless everyone has the flu, in which case everyone gets emailed the same ritual and we all perform it at home at around the same time to “link in” together.
As for full moons, due to scheduling issues, we gather only on weekends. (My High Priest is a union ironworker and is usually out of town on a build site M-F.) So we pick the “celebration date” that works best for us: Calendar Old Style, Calendar New Style, Astrological, or Signs. (Imbolc example: Feb 1, Feb 6/7, 15° Aquarius, when the first flowers break the ice.)
When the full moon falls on a Tues/Wed/Thurs, we usually pick a time in the evening when we can all perform the same ritual at distance. Otherwise, we celebrate on the weekend closest.
Now, for other rituals. I generally go with my gut. Something happens in the world, I usually let me covenors know, “I’ll be working X night at X time, anyone who wants to join me at the covenstead please let me know.” Sometimes a covenor will do the same, or ask me if they can call a ritual meeting at the covenstead.
We have a “private group” on Facebook where we arrange remote healing rituals, etc. Recently one of our number raced her Jewish Agnostic husband to the hospital mid-heart attack, and we worked like crazy on healing him. He seems to have come out healthier than he went in.
Then there are days when I just need to add a little boost to my connection. And I perform a Ritual.
Of course, I perform little rituals all day, every day. It comes naturally after a while practicing.
Timing of SPELLWORK is more intricate, but for rituals of celebration and communion, any time is a good time. ;D
Link to the original question on Quora.