Creance time is the time to make some guesses at the hawk's field response weight. I want to emphasize 'field' because I and apprentices I've known initially assumed that there is only one response weight.

At your home or mews the hawk will respond at a certain weight. That's because she's familiar with the surroundings, considers it the safe perch, and feels very comfortable there. She'll come to you at almost any weight there.

In the fields you use frequently, she has another weight which will be lower than the home weight. But these fields she considers 'her territory.' So when you take her to unfamiliar fields, you may want to take her down a bit more to ensure good response.

Other factors are weather, time of day and season. A hawk will often get very keen before a storm is due. Their natural hunting times are morning and late afternoon, with soaring and general hanging out in between. If you regularly fly in the afternoon, switching to morning (or vice versa) can cause some lack of response. The springtime often gets a little hectic because of mating season, not just for your own bird but your resident hawks who feel the need to stake out their territory.