It is very easy to measure the round-trip latency of your audio interface using a DAW and a digital cable.
Use these steps:
Open your DAW and select your audio interface driver. Create a track with outputs set to the interface DO (i.e. outputs 9 & 10). Select a clip with a sharp attack, like a snare hit. Create another track with inputs set to the interface DI (i.e inputs 9 & 10). Arm recording on the second track. Connect the digital ports back-to-back using a suitable digital cable. Use your transport bar to play & record simultaneously. You will see the clip recorded on the second track, delayed by the round-trip latency. Most DAWs have a 'delay' value that can be set on the second track. Use this to offset the record time. Continue changing the delay time & re-recording the clip until the two clips line up perfectly.
Your delay value will be the precise round-trip latency.
You can verify the delay with a null test. Invert the recorded track
& mix with the original; the samples will cancel out exactly.