The balance between shipping and perfecting the details is what makes things great. Last night I spent 3 hours on an animation for Cheddar. It was probably overkill to make a custom animation curve with CAKeyframeAnimation, but I really wanted it to look like what I had in my head.
Looking back at it today, I'm proud of it and glad that I learned more than I cared to know about animation curves. It might have been a better use of time to just use a default curve and finish the feature instead of spending the whole time on a single animation.
I'm still not sure if learning something new and perfecting it was better than finishing in this case. Usually whenever I spend hours on a particular detail (like fading in a slight shadow at exactly the right speed) I'm never sure which side of the spectrum it falls on. I think this feeling means you're doing it right.