Ditto is purpose-built for project based work. That's really the best way to use it, and it's what we recommend, in part because we're really big believers in value-based pricing.
That being said, if you prefer to bill hourly and still want to use Ditto, there are a couple of ways to approach this.
Option 1: Create a phase as though it is an invoice line item, complete with information about the number of hours you've worked and the total cost. Send it through to your client for payment. Once the phase has been funded, immediately request payment release.
Option 2: Work against a bank of hours. Have your client fund this "phase" of work up front, then track your time against the bank of hours over the course of the month (or whatever time period you prefer). If it looks like you're going to work more hours than your client has paid for in the project account, contact your client to discuss whether or not they'd like to fund an additional phase to purchase more of your time.