If the idea is simple, a 4-line poem can take minutes. More complex ones can take hours, days or even years.
I try to be precise with my metre (rhythm) and make sure that the stress is always on the right syllable. It’s beCAUSE (stress on second syllable) not BEcause (stress on the first).
I confess that when songs put the stress on the wrong syllable, it really grates me.
Once I have the ideas and the characters the hard work starts. The word has to be the right word — the perfect word. My rhyming dictionary and thesaurus are invaluable tools. Online versions can be useful but are seldom as comprehensive as my good old-fashioned paper ones.
The right word can hide away from me for ages. At the preliminary stage I generally don’t spend a lot of time hunting for that word. I leave a gap or put some question marks in so I don’t lose the thread of the story. Later on, the word may suggest itself or I may have to spend hours in the thesaurus or the dictionary trying to pin it down. If it continues to be stubborn I may end up changing that part of the poem altogether.
Later I go back and mark areas that need improvement and revisit them until it is exactly the way I want it. I’ve modified some words years later because a different word is better.
Do you have a specific way of finding the right words? Let me know in the comments section.