Sometimes the amount of network traffic, kicks the dongle from the high-speed HSDPA mode to the slower 3G mode, resulting in network time-outs.
normally, it shouldn't be too bad, at this time in the evening. Although that depends on how many others, are using the mobile networks at the same time as you.
Have you got the dongle plugged directly into the PC? I find its best to use the long cable, supplied with the dongle, so that I can place it about 10" away from the base unit. Also using the base unit to screen the dongle from the monitor etc.