The PICXO convergence time follows the standard rules for a second order PLL. The greater the damping, the longer the PLL takes to settle.
The less damping, the more the PLL will ring and also take longer to settle.
It also depends on what criterion is used to determine settling for the application.
The bandwidth time constant can be calculated using 1/(2*pi*f), with f being the bandwidth frequency.
In the spreadsheet provided along with the PICXO reference design, by default the graph plots the data point for -6dB.
For time constant calculation, use -3dB for better approximation.