Up until recently, you had two options:
- Don't set any timestamps anywhere, and let Adobe data collection servers take care of it for you. If Adobe sees any hits with timestamps, the hit is discarded. Almost all standard implementations use this method.
- You set the timestamps in every hit. If Adobe sees a hit without a timestamp, the hit is discarded. Many mobile app implementations use this method, due to its ability to upload hits after a mobile device has internet connectivity.
Recently, timestamp optional is a thing: Timestamps Optional
It allows some degree of freedom to send both types of hits in.
Bottom line is that if you aren't planning on sending hits to Adobe out of order, the least hassle option would be to simply let Adobe take care of all the hit timestamping.