We track the donation amount configured by the merchant and charge the credit card on file when $50 in donations is accrued or 30 days has passed, whichever happens first. Donations to nonprofits are disbursed within the first 15 days of the following month (so donations made in January will be received by the nonprofits by February 15th). 

The Pledgeling Foundation support site (link) has answers to many questions about how funds flow to nonprofit charitable organizations.