Investing time only won't actually work for new members. I know because Steemit was an experiment for me to actually see if it is possible to generate some Steem or SBD by not investing a single dollar.
As you probably know, things got a lot easier when I started using bots. I honestly think a minimal investment of at least $100 is required to have a nice start. The content quality will determine your earnings from there.
But u can earn that 100 $ too although it will take longer