A 4-bar phrase might take me half an hour to finish, if I’m working carefully and meticulously. it might have taken me twice or three times as long when I started writing.
That same phrase will only last 5 seconds when performed.
When we’re writing, time loses clear meaning, and so it’s important to step back and assess, using real time.
Set a metronome, sing or play the phrase you’ve been working on, and see how it actually sounds.
Does the writing you chose work in real time? Does the melody work in real time? Can we follow the harmonic motion in real time? Do you like it in real time?
It is absolutely true that sometimes, the things that work at the speed of writing do not work at the speed of playing. They don’t work in real time.