system.date.setTime(
system.date.now(),
system.date.getHour24(last_sample_time),
system.date.getMinute(last_sample_time),
system.date.getSecond(last_sample_time)
)
https://docs.inductiveautomation.com/display/DOC81/system.date.setTime
https://docs.inductiveautomation.com/pages/viewpage.action?pageId=58603995