There is typically about 4-5 months between the end of a drafted college player's senior season and the Aug 15 date for reaching free agency. It's a healthy chunk of time for the team that owns the player's rights to get him signed. It is true that if a college player is good enough, teams prefer to sign them some time before their senior season. However, that has more to do with the player being ready to take the next step in their development than it does pressure from an NHL club out of fear they will lose the player to free agency. College players who are determined to reach free agency are going to do so anyway, and just refrain from signing that contract with the team that drafted them.
Still super early for Tuomisto. He's clearly a kid who is going to play at least 2 years in college, and most likely at least 3. Too early for any hand-wringing over whether he might reach free agency. His development and proving that he was worthy of a 2nd-round pick is all that matter at the moment. He's a project (seems to be Yzerman's MO after the 1st round), but one with a fairly high ceiling. I'm not personally a big fan, but I try to give every prospect a fair shake.