Auto-translated
When excavating the Grail, the hero loses their entire turn. It is not allowed to excavate the Grail on the day of arrival at the location of future excavations. However: There is one caveat that is quite thoroughly discussed in one of the topics on HeroesPortal - "A puzzle from Arkh." The essence of the caveat is that there is a method that allows you to excavate the Grail on the day of arrival by varying the hero's maximum MP level. Details can be found at http://www.heroesportal.net/tavern/?id=150632.
I read about this trick in the physics section, went to the forum, and found out that someone suggests transferring a slower unit to the hero before excavating the Grail, and this should allow you to excavate the Grail even if you don't have a full turn. However, despite all my attempts, I couldn't make it work in SoD. Maybe I misunderstood something?