Advanced frame timing using XrTime?

Hi. We do not want that the return of xrWaitFrame is delayed because previous frames had less render time. We know that is to minimize latency, but we have our own render time throthling. Therfore we would like to call xrWaitFrame as late as possible. We will delay the call if our renderer is ready early.

The question is: how do we know how long to wait? We know there is a XrTime. Is there some function that relates this time to frame boundaries?