I'm not too familiar with the VIs used in this driver, but there should be a way to share a clock/timer between the channels. Take a look at the Advanced Sweep Example and see if you can gather anything more from how the manufacturer uses triggers.
If you don't see a way to do this, you may just want to add a delay to the channel that is going first. From what I can see, you may be able to use the Config Measure Settings VI to do this
Regards,
Joel I.
Applications Engineer
National Instruments