Very hard to say.
If you have made sure they have recently logged in, they might answer it the next time they log in, providing they are interested in answering it. But we've all made the mistake of sending messages to people that haven't logged on for about a year when we first joined. But if they are hot chicks then probably loads of other men have contacted them, so you have to send messages that stand out, and will probably take them longer to answer..

I`d say a week is long enough to know if you`re getting a reply, some people work away from home all week etc. Plentyoffish.com shows you when your sent messages have been read and/or deleted which is a good sign

Does that here too.

with phrases like 'hot chicks' and 'stunners' I think I have stumbled onto the 1960's version of Flirtbox!