When a business has the "flex-start" option on their Ops, it means that the Operator assigned to the Op will have a time arrival window to the Op before they're disputed as a "no-show" or sent back home without performing any work due to tardiness.
For example, the Op's schedule could be from 8 am to 4:30 pm with a flex start time of 8:15 am to 4:45 pm. Essentially, the Operator can arrive at 8:15 am at the facility, however, they will need to stay until 4:45 pm in order to be paid out the full amount (otherwise, the business can adjust the payout down if the work was not completed).
As a best practice, we recommend arriving at an Op a few minutes before its start time to avoid any issues with checking in and out (or with the payout). Being on time also leaves a great impression on the business of your work ethic which could, in turn, result in being invited back to work with them.