The syntax looks as following:
DELETE FROM t FOR PORTION OF <apptime> FROM <FROMVAL> TO <TOVAL>
For the case when row period is not totally inside <FROMVAL>...<TOVAL>, then the deletion should act like DELETE+INSERT (or two INSERTS if needed) was done.
This is important if we have DELETE/INSERT triggers.
If not, then more preferable way is to minimize the DELETE operations (in favor UPDATE ones)