as the subject - is there any way that this can be done?
(I have successfully created a new project in billings and linked back to daylite, as well as sending a project from daylite to billings)

You can send a slip to Daylite, which will create a task or appointment as selected, and link it to the contact in Daylite. Is this what you're looking to do?

We have demonstration movies on the Billings 2.5 site at http://www.billings2.com/daylite/.

Unfortunately, using these two together is riddled with issues. There's no way (that I know of) to send existing projects from Billings to Daylite. While you can send time slips from Billings to Daylite, this leads to the loss of timer records since Daylite doesn't support time slips. The time slips will be converted to Daylite tasks and dissociated from their project, you will need to relink them with it. Once you do that and update your project in Billings, they will be reimported but the timer data will be all lost and the amounts will be calculated based on finish time minus start time - i.e. massive over charging!

Billings should be a regular feature in Daylite that could either run alone or as a part of Daylite using its database, introducing time slips as a concept in Daylite, that would solve these problems.