S2member search user by data


I’m developing for my client, a simple software in php, where my client could search user by inserting date and type of membersip.

For example: I want to see what are the number of Free membership between 1 June and 30 June.
I’ve seen that there is the timestamp for every user in wp_usermeta, but in Json format (maybe?) with other data.
How I can set a “between” for this case?