How long does a normal game of Monopoly, with 4 players, last?
In my playgroup (using the base rules, no house rules), our 4-player games take about 90 minutes depending on how intently we're focusing on the game instead of just hanging out.
In addition to the common house rules that extend the game, certain strategies favor long, drawn-out games. Anecdotally, if everyone plays &quot;not to lose&quot; and refuses to make deals or bid on contested properties, the game can drag on. But if people are playing to win, the game goes much more quickly because of how much Monopoly snowballs. Most moves made to win are high-risk, high-reward. These games end rather quickly, with a player eventually just dominating the board and snapping up property at bankruptcy auction.
Here are some play style adjustments that can lead to shorter games:

Put more property up for auction. This will often lead to players draining their resources more quickly, which will allow for faster bankruptcy.
Make aggressive deals to get monopolies, even if you think you're getting a &quot;worse&quot; monopoly. The key thing to remember is that a deal that gives two players monopolies helps both of them overtake the remaining two opponents. You go from ~25% to win a slow game to ~50% to win a two-player slugfest.
Build houses aggressively. The best way to bankrupt others is to get the cashflow snowball started by building houses. The first and third houses are particularly important. The first house greatly makes rent cost a relevant amount (and help you build future houses), and the third house will often be enough to bankrupt players.