>>530469302
well, mettaton only recently took over that apartment to turn it into his hotel, so recently there are still people living in it

in my estimation it's been at least a year. we go from mettaton built> alphys starts experiments ->alphys fucks up big -> mettaton now a BIG SHOT -> alphys stews in her own depression for a long time

it's also implied flowey has just been waiting around quite a while before you show up.