@Piru
Hey 8-) Well, I'm reading the RKM Devices on the DevCD2.1 (the HTML version). Never saw what you posted there on the timer device chapter.
What I said above I found on: reference/HTML/Devices_Manual_guide/node00C0.html
It says, regarding VBLANK:
"The VBLANK timer unit is very stable and has a granularity comparable to the vertical blanking time. When you make a timing request, such as "signal me in 21 seconds," the reply will come at the next vertical blank after 21 seconds have elapsed. this timer has very low overhead and may be more accurate then the MICROHZ and ECLOCK units for long time periods. Keep in mind that the vertical blanking time varies depending on the display mode."
And regarding ECLOCK:
"The ECLOCK timer unit uses the Amiga E-Clock to measure the time interval you request. This is the most precise time measure available through the timer device"
That's all I can find there and I've read the whole chapter about the timer device. Maybe the HTML version lacks some things ? I'm using it cause my Amigas don't have CDROM ATM...