Sorry for the confusion - PTD is of course right - I don't know where I got the crazy idea that the EPG always shows a full 8-days (i.e. 192 hours). It'll always only show upto midnight GMT on the 8th day. So, at 00:01 BST on Monday (i.e. 23:01 GMT) you'll basically have 7 days and one hour available in the EPG. At 01:00 BST this would have changed to the full 8 days including all of the following Tuesday.
However, it won't download a whole day at once, literally, as the EPG is constantly broadcast in a carousel format - as you may have noticed when switching on from low power standby (i.e. the channels/days gradually fill in a kind of random manner - for example, you may have 8 days of BBC1 within a minute, but nothing showing for the current day on ITV2, yet the ITV2 listings for the next day are shown). It takes a little while for all this information to be read and pieced together like a jigsaw to form the full EPG.
It is the fact that the EPG is constantly being broadcast, which the Vestel software is constantly monitoring, which causes it to access the HDD and timers (and the software slowdown IMHO) even if it doesn't involve setting a new timer, but just confirming an existing one. This is in contrast to the 4TV EPG which was downloaded in full only at 3am every night, IIRC. The Freeview EPG is better in that it can change live - particularly on BBC channels you'll find the EPG is updated immediately if a programme overruns, for example, causing the schedule to be changed.