God is omnipotent, which is all powerful, and omniscient, all knowing. He is, of course, other things too; I just gave these as examples of omni- words. Omni, in Latin, I think, means all. Is there an established omni- term for "everlasting" or "eternal"?
Eternal is a Latin word
late 14c., from Old French eternel "eternal," or directly from Late Latin aeternalis, from Latin aeternus "of an age, lasting, enduring, permanent, everlasting, endless," contraction of aeviternus "of great age," from aevum "age" (see eon). Used since Middle English both of things or conditions without beginning or end and things with a beginning only but no end. A parallel form, Middle English eterne, is from Old French eterne (cognate with Spanish eterno), directly from Latin aeternus. Related: Eternally. The Eternal (n.) for "God" is attested from 1580s.
If you are looking for a word that says "omni" you could try to coin "omnitemporal," but eternal has better usage. Sempiternal means "always", but again, not and "omni".