When I worked as a rental broker many people would call me as early as 6 months in advance and as late as day-of to find a home. What is the perfect window to start your search? Generally about 6 weeks before you want to move in. Some listings do pop up far in advance of that, but they are in the minority. If you want to casually start looking online to get a gauge of pricing and what is happening, then sure, start earlier. But for actual rentable, available apartments—they won't really start showing until six weeks before, with the most availabilities showing up on the first of the month. This happens because many renters don't let their landlords know if they will renew their lease sometimes up until the last minute.
Searching too early or late for an apartment.