I'm an alien. I made a bet with another alien, that I can:
Stay on Earth for at most 100 years.
Start a religion
It may be based on existing one, but be meaningfully different.
E.g. Latter-Day-Saints (Mormons) vs. mainline Protestants counts. Different versions of Anabaptism are not "different". Sunni vs. Shia counts. Reform Judaism vs. Orthodox one counts, but reform Judaism vs. Reconstruction doesn't (not meaningfully different enough).
Have that religion last EXACTLY 500 years (give or take 5 years, but your bet pays much more for more precision). Anything outside of 5 years margin, you lose.
Bet conditions prohibit you from actually specifying 500 years anywhere in the content of your religion. Or any specific dates 500 years in advance.
Bet conditions prohibit you from interfering IN ANY WAY with that religion beyond initial 100 years.
This, among other things, means you can't leave a miracle generator with 500 year battery, and predicate the religion on miracles keeping coming.
You can't change people from regular Homo Sapient biologically.
No raising their lifespan to 500 years. No ticking biological timebombs in their genes.
You can perform modest "miracles" using "magic" alien tech, that are confined to, say, the scope of what Jesus Christ or Mohammed was reputed to have done (modest matter generation, modest energy generation, some advanced medicine for few people. Mass-depressors to ensure your followers can succeed in attacking an enemy city or two; but no super advanced weapons - and especially no super advanced weapons left in human hands for 500 years).
ALL your miracles must expire in the 100 year period - no verifiable trace of them should be left once you leave earth except hearsay or naturally-looking consequences.
What can you do to structure your religion, so that it lasts 500 years BUT doesn't last beyond that, guaranteed? Not that it should matter, but the bet is pretty-high-stakes, let's say 100x average lifetime salary if you win, and lifetime of indentured servitude if you lose. And you can't get out of it.
Timeframe is flexible, you get to pick anything in recorded human history (so, let's round to 2000BC to 2000AD).
You have approximate knowledge of how Earth history went in that entire time period, meaning you can engineer your religion and your timings to co-incide with major trends.
BUT, you have only approximate knowledge (because of butterfly effect, or because your psychohistorical formulas have a large error margin, whatever) - Columbus may have sailed to New World in 1492, OR in 1481, OR in 1511. Or he may have died at birth and another dude discovered New world 50 years later. So you can't simply say "found a religion in MesoAmerica 500 years before Cortez and hope Cortez wipes it out for you in just the right 10 year timeframe to win the bet". Remember, allowed margin of error is +/- 5 years.