The Salesforce Nonprofit Success Pack has a Recurring Donations object designed to aid you in forecasting and tracking donations. When a Soapbox Donation record is converted, the conversion process will create a new Recurring Donation record and associate it with the Soapbox Donation Opportunity.
The creation of future "Pledged" Opportunities in accordance with your NPSP Settings under Recurring Donations is not triggered immediately upon creation of the Recurring Donation record. This happens during a nightly batch process. You can, however, trigger the batch update in the Nonprofit Success Pack by going to Nonprofit Success Pack Settings > Bulk Data Processes > Recurring Donations Batch and clicking Run Batch. This will force the update immediately.