This is typical, and is expected by enterprise customers. Additionally, it's expected that 1 billable day could end up meaning anything from 5 minutes telling a staff tech which wire is crossed, or 15 hours working an exceptionally challenging problem. ymmv, and it all evens out in the end. If you feel like you're getting the shaft over the course of several projects, that's when you know it's ok to raise your rate (or that you need to improve your skills).