You can schedule a show ahead, and people who follow you are told when it starts.
Regularity beats timing
There is no universally best hour. There is only your buyers' hour, and you find it by being on at the same time repeatedly and watching what happens.
A seller on every Sunday at eight will beat a seller who appears at cleverly-chosen times nobody can predict. People plan around things they can rely on.
Announce it
A scheduled show is a thing people can be reminded about. An unannounced one is a thing they have to stumble into.
Tell your followers. Tell the people at the end of your last show — "same time next week" is the single most effective sentence in a seller's vocabulary.
Give it a title people can read
What is in it, not "Sunday sale". "Stoneware and seconds" tells somebody whether to set a reminder.
Questions people ask
How far ahead should I schedule?
Far enough that people can see it coming. A few days is plenty.
What if I have to cancel?
Cancel rather than leave people waiting — the cost is to the people who set a reminder, and they are your best buyers.
Does the time of day matter at all?
Less than consistency. Evenings and weekends are where most people are free, and that is about as specific as honest advice gets.
What if nobody comes to the first one?
Normal. What actually changes it.
Next: your first live show.