WordNet sense 1 (direct in spatial dimensions; proceeding without deviation or interruption; straight and short):

direct

WordNet sense 2 (at all times):

around-the-clock, round-the-clock, day-and-night

WordNet sense 3 (continuing in time or space without interruption):

continuous, uninterrupted

WordNet sense 4 (a flight made without intermediate stops between source and destination):

nonstop flight