Not greater than operator for time in WHERE clause

I need to select my fields which have values only before now()-4h and not after that. But, the query SELECT field FROM measurement WHERE time<now-4h also shows the fields which have values after now()-4h, because they also have values before time<now-4h.

So, in this case I need something that will check time ! > time-4h (not greater than).

Any workaround or suggestions or ideas are welcome.