Filter Condition for custom field in account record

Hi experts,

I would like to count the number of cases created in the past 90 days and display on a field in the account record. 

I have tried the same via a rollup field but I cannot add the "created on: past 90 days" condition because there is no "Last X Days" option in rollup field:

Can I accomplish the requirement via javascript web resource? Kindly help with some sample code if possible.

Thanks,

Jon