Coming from premiere - I just watched a little tutorial and I've got the basics sorted: I've dragge my keyframe for the end of the clip from 8 mins to 1 min, but I've got part of a clip that I want to play at normal speed 25fps in this case. I've added 2 new keyframes and stretched that secion back out again but have no idea what the fps is. Its easy to ramp the speed up but I cant see an eloquent or easy way to get it to play at normal speed.
If things get confusing, simply split the clip in multiple layers/ segments. Nmowhere does it say that you need to do everything on one layer. Still, I don't quite see your problem, you just went ahead too quickly. By default time-remapping will create a start and end keyframe and they will ensure it plays at its native speed. Therefore adding more keyframes inbetween would ensure the same. So basically you should have added your segment with the constant speed first, then re-arranged and added more keyframes on the timeline after you have made sure your segment plays like you want....
gotcha: so you select the part to stay constant speed - keyframe it, then add more keyframes at the start and end and drag them towards the bit that at the right speed.
(I ended up fudgin it by nudging the keyframe position incremnetally until I could see there that it was playing each and every frame - tedious but I got there in the end)