You make money in Millionaire City by collecting rent. Longer lasting contracts will yield a higher amount of rent when it is time to collect.

Each contract has a different amount of leniency before the tenants abandon the property.

3min --> 1h
30min -> 1h
1h ----> 1h
4h ----> 4h
8h ----> 8h
12h ---> 12h
1d ----> 1d
2d ----> 2d
3d ----> 3d