Derek, my following comments are just for consideration of all. It's not directed to you. I find I need to offer disclaimers like this because some take my general comments personal and I don't mean for it to be that way. Often questions from sharp contributors like you trigger a thought I would generally like to share.
This is my perspective on frost-seeding. I think the idea and expected results are misunderstood. When water freezes its volume expands. When it thaws it contracts. Works the same way in the soil. Freezing pushes soil particles apart, vice-versa for thawing. This automatic expansion and contraction is a gift giving seeds movement into the soil where they belong. Some seeds do better than others. So, frost-seeding should occur when there are cold, soil freezing temperatures followed by clear days where the sunshine reverses the overnight soil freeze, Soil expansion and contraction, opening and closing.
Where I am we frost seed but we hardly ever have the right situations for it to provide any benefit over simply broadcasting at the right time. In Lycoming County PA I would think now would be an ideal time to be doing it. April seems to me to be too late. I think I would want to do it earlier rather than later but after a winter period where the soil is frozen solid for an extended period of time.