Tomorrow night the Greenmantle in Newington (near Scayles music shop) has a Shetland Spring Festival from 9pm on, with Shetland rum, bannocks and maybe "white wife" (a local Shetland beer named after a mythological figure from Yell). I think the landlady of the Greenmantle is from Shetland. The Greenmantle hosts a Shetland fiddle music session on Sunday afternoons, so maybe there'll be some Shetland music tomorrow night as well.

The same evening, later, is the Edinburgh Beltane Fire celebration on Calton Hill, which goes on till dawn:
Beltane Fire Society

I'll probably be at the Greenmantle, I have to get up for work on Saturday so the Beltane Fire is out.