In most cases, doubling that first cool million is going to take some time, but it’s also not outside the realms of what most people will be able to achieve through a normal experience with the game. However that does require the entirety of those 4-5 hours being spent grinding money rather than doing other more fun activities, and you need to have invested in certain businesses already to reach that hourly income.
If you’ve already invested heavily in the game and put all your effort into grinding money in the most efficient way possible, you could earn this in about 4-5 hours as we explored in my previous article on how to make money in GTA Online. For the purposes of this discussion I'm going to set a hard limit of two million GTA dollars.