you don’t need to use any function to cast a string to date/timestamp
just type select * from table where date_fied = ‘yyyy-mm-dd’ or select * from table where timestamp_field = ‘yyyy-mm-dd hh24:mi:ss’ and the engine will do an implicit cast. so in your case
where "time_sell" < '2000-02-01'
you can read the supported date/timestamp formats here
in the paragraph Accepted Date, Time, and Timestamp Formats you will find allowed formate for date/timestamp, in the paragraph Date/Time Function Support the functions to manipulate date/timestamp fields
if you want to use an explicit cast you can add date or timestamp keyword before the constant
select * from table where date_field = date ‘2008-10-01’