Adjectives

(s)timelybefore a time limit expires“the timely filing of his income tax return”
(s)timely, seasonable, well-timed, well timeddone or happening at the appropriate or proper time“a timely warning”, “with timely treatment the patient has a good chance of recovery”, “a seasonable time for discussion”, “the book's publication was well timed”

Adverbs

(r)seasonably, timely, well-timed, aproposat an opportune time“your letter arrived apropos”