Sadly outside of cities or campuses its harder to do, however...
"Be at my house at 5:30am saturday if you want to hike."
"Come over tomorrow at 11 if you're interested in brunch, I'm making [...]"
Upon meeting people will say "we have supper on Thursdays," which I think is essentially an open invitation one day a week to stop by.
“Delighted to see you,” said Princess Shtcherbatskaya. “On Thursdays we are home, as always.”
and later:
“Delighted,” he said coldly. “On Mondays we’re at home. Most fortunate,” he said to his wife