Hence does not always mean from now; it can mean in the future or later or even from then. From the OED:
hence adv.
II.6. At a specified time from now; at some point in the future.
Source: Oxford English
Dictionary (login required)
Grammarist shows one of hence’s definitions as From now, from that time.
Although the OED’s seven usage samples all are of the sense of from now, and despite what the dictionary thumpers say, the corpus shows plenty of samples where it does not mean from now.
Here are some of the many samples from the Corpus of Contemporary American English (forgive me for offering so many, but I wanted to erase any doubts around anomalous or non-idiomatic usage):
The economy of the United States in the middle of the nineteenth
century was sharply divided, on a line along which the nation itself
would nearly cleave a few years hence.
(MAG: American
Heritage, The Business of America. Gordon, John Steele)
Predicting market prices and the cost of technology 20 years hence has
proven near impossible for just about everyone who as tried over the
past 50 years.
(WEB: Scientific American, A Solar Grand
Plan)
In 2008, when the US National Intelligence Council issued its latest
report meant for the administration of newly elected President Barack
Obama, it predicted that the planet’s “sole superpower“ would suffer a
modest decline and a soft landing fifteen years hence.
(WEB:
TomDispatch, Bill McKibben, The Most Important Story of Our
Lives)
The story starts in the spring of 1992, as Salt Lake City was gearing
up its campaign for the 2002 Olympic vote three years hence.
(NEWS: USA Today, Beyond the investigation Kim inquiry closed with
questions unanswered. Mike Dodd)
Heroin would come years hence, as would a near-fatal overdose.
(NEWS: Chicago Sun-Times, How street kids live. Mike
Thomas)
Lopez Rega was not there when I phoned, but when he returned my call
we agreed to a date at ten in the morning two days hence.
(ACAD: American Scholar, Orange juice with General Peron.
Falcoff, Mark)
He knew not what to make of the encounter. Nearly two years hence, it
haunts him still.
(MAG: Rolling Stone, When your name is a
punchline, you live in hell. Barry Manilow lives in hell. Zehme, B.;
Risko, R.)
But just six days later, on August 11, the Watts race riots broke out
in Los Angeles, leaving 34 dead. And six days hence, on the last day
of rioting, the Moynihan Report on the break-down of the black family
was issued to a firestorm of verbal violence.
(ACAD:
Commentary, Moynihan. Siegel, Fred; Cove, Peter)
They all made bail and went home to await arraignment a few days
hence, alongside other men who were charged with writing bad checks
and fishing off the wrong Sarasota bridge.
(MAG: Rolling
Stone, Who killed Pee Wee. Wilkinson, P.)
Eventually, Joy’s reputation and stature were more or less
rehabilitated. And ten years hence most of what he’d been lobbying for
was part and parcel of colony policy.
(ACAD: Humanist,
Original Intent. Braasch, Sarah)
She married in 1835 and moved with her husband to Galveston five years
hence.
(ACAD: Journal of American Ethnic History Southern
Jewish Women and Their Social Service Organizations. Bauman,
Mark)
Perhaps there was even peace to be made in the family, years hence
when the old man emerged from prison and therapy.
(FIC:
Fantasy & Science Fiction, The movements of her eyes)