Yes, it is usually intended as a monthly payment, BUT the actual UBI (in theory) doesn't (and shouldn't) pass through a "means test", i.e. (still in theory) it is "Universal" and as such all citizens should get it regardless their income or estate, as the Wikipedia article highlights:
>This article is about the system of unconditional income provided to every citizen. For the means-based model of social welfare, see Guaranteed minimum income.
https://en.wikipedia.org/wiki/Guaranteed_minimum_income
also sometimes called "basic income" (without the "Universal")
which is more pertinent and actually the one on which some (mostly failed) experiments have been done or are being made.