Membership purchase after visitation

Hello!

I am hoping someone in a similar situation has cracked the code on this, but I am looking to see how many people, who visited the Museum in a particular period, using a particular price type, purchased a membership after their visit and the average time between visit and membership purchase. Our memberships are booked as tickets in a different title than the admission tickets which is important context. Originally, I did:

([Order Days in Date],[Title of Membership])-([Order Days in Date1],[Title1 of General Admission], [Price Type contains "+all")

However, that clearly does not work as the days in date field in Analytics is not a numeric value. Any ideas on how to covert the date fields into numeric values with a filter would be apricated!

Thanks!

Rhiannon