How are you supposed to sell "on close" price ?

[lemanioc@xxxx]

Hi,
on many test system you test your trade and you decide if you want to 
exit on open or close of a given day for example.

How am I supposed to exit on close price ? If the market is closed, I 
will not be able to place my trade at that price. Do you expect to 
make the trade on post market ? Tomorrow ? Are these measures 
reliable ?

In brief, how to you sell on close price ?

Thanks,
Manioc