HotSpot - Long time to log in

Hi!
I’m new to HotSpot, and don’t know how to handle this…
Every time a customer wants to connect to my hotspot, opens the browser and has to wait for 30 seconds or more to see the log in page. Sometimes they connect and leave the PC untouched for a while, and when they want to use it again, it takes minutes for the hotspot to reconnect them!
Why is that?
What should I look for?

My connection schema:
Internet → HotSpot PC → ( ether - RB532 bridge - wlan ) → ( wlan - RB112 bridge - wlan ) → ( Wireless client - Notebook )

A friend told me not to use cookies, so I have disabled them, but I don’t think that has much to do, it should work well anyway…

Another friend told me to look ARPs, but I haven’t found anything there yet (not sure what to look for specifically, yet, nothing strange)
By the way, all bridges are rstp enabled. RB532 transmits on 5.8, RB112 bridges from 5.8 to 2.4, and customers log using notebooks with wireless interfaces to the 2.4 open signal.

Any hints?

Hmmm, it seems to have something to do with DNS…
Look here: http://forum.mikrotik.com/t/static-dns-failure-on-hotspot-cant-load-login-page/16183/6