Your son can reach out at any time, there is no restriction recruit contact, just restrictions on what type of communications and information a coach can respond with so your son initiating contact is not an issue.
Men’s Rowing is not an NCAA Championship sport so technically schools do not have any restrictions though they typically follow the regular NCAA rules. The general rule is “prior to the students” junior year so I believe that they would be able to respond without issue but others know rowing far better than I.