Olympus 5060 sleep mode is frustrating

As stated in the manual my 5060 goes into standby mode after about
3mins. That's a pain when I'm trying to be ready for a very quick
photo at any time, or for times like lining up a shot on a tripod at
night.

According to the manual I can press any key & it comes back to life.
In fact the zoom button seems to work ok, but others have no effect.
Rather than being an instant-on, the camera can take between 5 and 30
seconds before the LCD screen comes back on, with the lens sometimes
zooming in and out. This is real frustrating!

Once it has been in sleep mode, it seems to go back to sleep very
quickly - perhaps in just a minute.

Anyone with a 5060 got different behaviour, or any suggestions?