Yes, ingesting sensor readings for the future is possible, but not into the unlimited future.
To provide a buffer for time synchronization between our server and the device clock we allow to post data up to 60 seconds early. What goes beyond 60 seconds is rejected.
What does this mean? If your device clock is e.g. 30 seconds early and posts a measurement for e.g. 12:15:10 and it takes 5 seconds for the message to reach our server then it posts data at 12:14:45 for 12:15:10 – which is still ok.
So you should make sure, that the device that adds the timestamp is synced once a day such that it will be always within seconds of the server time.