That's a good point. It was famously the preferred policy of Milton Friedman (presumably as a cheaper alternative to the welfare state, back when the Overton window was still more FDR than Reagan). A negative income tax might need to be paid out weekly or monthly to make a meaningful difference to the homeless and the working poor (to say nothing of access to banking services; as long as we're waving policy magic wands, let's add postal banking to the mix.)
Of course, I feel obliged to bring up the Georgist objection: that either negative tax or UBI would need to contend with the problem of ground rents, lest landlords simply jack up the rent by the $X additional income that they know for a fact that everyone has.
Fun aside: Thomas Paine, the author of "Common Sense", made one of the earliest proposals for a citizen's dividend [0] (funded by ground rents), but going the other direction: a one-time lump sum during young adulthood, as a means to bootstrap a homestead or small business.