According to their twitter accounts (see below) both are flying to Arizona today (Monday).

‏@m_agosta17 - Off to AZ tomorrow! ‪#journeybegins

@mwilliamson7 – Off to Arizona! I will be a Giant soon! Thanks to every single person that has helped me get where I am today!

If you go to Agosta's twitter page, you'll see that he's already updated his profile:

@m_agosta17

Pitcher in SF Giants organization

If they follow past tendencies, both guys should be getting their medical exams today, and the Giants will likley be announcing both signings on Tuesday. I also think that we'll likely to be seeing Stratton, Agosta and Williamson making an appearance at AT&T Park and being introduced to the fans at some point later this month. They'll probably pay to have their parents flown out and give them the full-court press and red carpet treatment.

Agosta pitched a lot of innnings as a starter for St. Mary's this spring, so I don't think we should expect much more than some bullpen work from him this summer. I would guess that he ends up in Salem-Keizer with Chris Stratton, but he could also stay in Scottsdale if they want him in a more controlled environment. The Giants will likely keep him from making his pro debut for at least 3 weeks as they slowly work with him to get his arm into game shape again.

Williamson should be ready for his pro debut much quicker. I think he'll be on the field again in about 10 days - most likely with Salem-Keizer.