how much is the hourly lounge to stay at beijing airport? how long can you stay at a time?

Do you stay in T3?
As far as I know, there are two kinds of hourly lounges in T3, Business travellers lounge T3-E and Hourly lounge T3-C, which charge in different prices.
For the first one, it charges 180RMB per hour for a standard room if you stay no more than 5 hours and 980RMB for the whole day.
For the second one, it charges 100RMB if you stay there one hour. If you stay for two hours to four hours, the price vary from 150RMB to 360 RMB for differet time and different rooms. If you stay longer, the price is different, too.
I think you can refer to the official website of Capital Airport for detail information.
There is no certain limitation for staying time, but if you just stay for several hours, it is OK.