I was driving Grab full-time for 2 weeks last month while waiting for school to start, so I have some experience.
I drive Grab about 14-16h a day, 7 days a week, typically from 7am-1pm, then 3pm-1am. The peak period starts at around 7am, if you start earlier, there’s a chance you might end up in CBD too early and have to go back to the heartland area for better fares.
After lunch, things start to quieten down a bit and pick up again at about 4pm, so if you want some rest or shut-eye, this is the best time to do so. The evening peak hours and nights tend to be better in terms of job availability, and I normally drive until I get a job that brings me closer to home, and then go offline from there. On a typical day, I drive about 400-500km doing Grab.
By doing so, I earn a revenue of about high $400s to low $500 a day, but it can sometimes get up to high $500s if it’s your lucky day. After deducting rental ($87/day), petrol (~$30/day) and commission (20% of fares which is about $80-$100), I can take home about high $200s to low $300s a day, which works out to be about $20/hr of profit. However, I have to say there is quite a fair bit of day-to-day variability, which I cannot account for since I have not driven long enough to notice a trend. Perhaps other drivers can help you better there. In the 16 days I’ve worked for, I earned about $4000, and if you maintain for a month, it shouldn’t be difficult to earn about $8000, given that there are some days that I did not drive Grab a full day.
As for the Grab incentives, the most recent update severely limited what we can earn in terms of incentives, with each gem (think of it as points) giving you $0.40, instead of about $0.85 last time. They also have a rental rebate, which gives you back 6% (I think) of your fares to offset your car rental.
GoJek is definitely better for incentives compared to Grab, esp the most recent one. If you hit the max target in a day, you get an extra $205 of profit, which is certainly doable if you drive the whole day. They recently upped the incentive, but I haven’t checked it out in detail, so I can’t help you there.
However, I do have to agree with what the others have said. GoJek’s matching seems to be quite flawed compared to Grab, as I had a few jobs where I had to drive about 10 minutes to get to the customer, and there is some waiting around involved during the lull hours. The fares seem to be lower on GoJek as well, but to put it in another perspective, regardless of whether you drive on Grab or GoJek, the fares of the jobs you get will always be lower since most customers are price sensitive and would opt for the cheaper option anyways.