constant

fast, fixed, hard-and-fast, immutable, inflexible, invariable, unalterable, unchangeable

established, set, settled

ceaseless, continuing, durable, enduring, lasting, permanent

continual, intermittent, recurrent, recurring

cyclic (or cyclical)

around-the-clock, hourly, round-the-clock

chronic, confirmed, inveterate

expected, usual

dependable, dutiful, reliable, responsible, solid, tried, tried-and-true, trustworthy, trusty

unfaltering, unhesitating, unwavering

determined, intent, resolute

confirmed, dyed-in-the-wool, inveterate, sworn

ardent, avid, enthusiastic, fervent, fervid, gung ho, impassioned, passionate, serious