I want to buy/short at whatever the open price of the day i. E. At 9:15 and not in absolute value. Just want to specify to buy at the open of the day

Throw a Buy order before market opens, to buy at the open of the day i.e at 9:15 without specifing buy price in absolute value.

i think ur queries can be solved through after market order

check it in order>after market order

i also want a script for it, or a alert to buy on one click