How much time does it take to cook a nice poem? I'd say as long as it takes. One should not rush through the preparation process just for the sake of completing it. Cooking takes time and so does writing a poem. Remember how your mother cooks the best dishes for guests but struggles while cooking just for the sake of it (ignore if your mother is the best cook in the world :P). Give the poem enough time; no one likes to eat a half-cooked meal.
"Wine is bottled poetry." ~ Robert Louis Stevenson
Sometimes, it is better to keep a poem unfinished and return to it at a later time; maybe after a few hours or days. I don't mean you should wait for years to finish a poem, although some poems might take years to reach their final form. Slow cooked food tastes the best.
Poetry is too beautiful to be grammatically incorrect. English is not my first language and I make a lot of grammatical errors while writing. I am not a grammar nazi either. You can always check your grammar on some sites. Personally, I use Grammarly which is a chrome extension. It is not too trustworthy though and I always refer to a dictionary whenever I am in doubt. Finding a grammatical mistake is like finding a hair in your soup. You might be forgiven if it was the first time. But guests would certainly be reluctant to taste your food again, if they find one hair after the other. Know the difference between "there," "their" and "they're."
"There are three things, after all, that a poem must reach: the eye, the ear, and what we may call the heart or the mind. It is most important of all to reach the heart of the reader.'" ~ Robert Frost
You might be surprised (or not), but poetry is meant to be read aloud. I consider recitation as the ultimate test of a poem. A cook should always see, smell and taste his own dish before serving it to others. Is the salt/sugar alright? How does it smell? Mmmmm...the lovely smell. Finger licking good!