mark-in/set duration/mark-out in clip browser?

When I select a clip in the browser, I can go in and mark in/out using the playhead and my mouse, but is there a way to mark-in, then type in a desired duration, and mark out? Let's say I have a photo that I want to use. Instead of going in and hitting "I", then playing (or scrubbing forward 5 seconds) and then hitting "O". it would be great to just hit "I", "+5.", "O", and then "E", but it doesn't seem to work in this manner, and I'm wondering if its something I am missing or if its designed this way.