A sweep cannot be stopped by an input into a stop channel, but there are several ways to measure time differences between two channels:

- In the hardware settings dialog, there is a checkbox "time differences". It can be used together with "endless" sweeps. The reference channel can be selected as either CH1, CH2 or CH6 (=START). The time spectra show then the counts versus the time difference to an event in the reference channel. See in the manual page 5-6:

An acquisition mode "Time differences" is implemented for analyzing pulse trails. In this mode the first stop event is used as a reference point and for following stop events the time difference to the reference is calculated. The displayed spectrum is then a relative time distribution of stop events related to the reference point. Even wrap around mode works in this differential mode. The first stop event that falls out of the chosen time range after a reference event is taken as a new reference point.

- You can do normal sweeps and create a dualparameter spectrum for example A1 x A2, by opening the Spectra.. dialog and "Add Multi". In the dialog defining the Multi Display Setting you can define the 2d dimensions range and a Threshold for each channel. The Threshold is a minimum time difference between the stops measured in elementary dwell tiime units (usually 100 ps), the first stop after the time threshold increments then the corresponding (x,y) point in the dualparameter spectrum. Further events within the same sweep are not shown in the dualparameter spectrum. I think especially the dualparameter spectrum is what you are asking for.