Is it even possible to use a processor other than PayPal flow with IFS?

Your only other option is to use Cybersource as a gateway.  We are currently using Cybersource on IFS Cloud with good functionality - happy to help answer any questions.

Would you be able to estimate in hours or days how long it took to change over/implement Cybersource as a gateway?

I can’t accurately quantify time as we largely did this during implementation and UAT, but IFS Cloud had most architecture in place for a plug and play operation.  I’d encourage you to utilize Cybersource’s Sandbox environment for testing and implementation.

In full disclosure - we did run into several issues with how cards were being processed including improper authorizations and duplicate charges which easily surpassed the total time for setup/integration ten-fold, but all of these issues were supposedly fixed in future releases.  

There is a credit card user guide that has been published by IFS and it outlines the setup pretty well.  Attaching here for reference.

Thank you!