For that matter, using the temporal join also didn't seem to produce watermarks:

reate view test4 as(select *, current_watermark(test1.order_time) as curr, if(test1.order_time > test2.order_time, test1.order_time, test2.order_time) as mt from test1 inner join test2 FOR SYSTEM_TIME AS OF test2.order_time on test1.product = test2.product);