its all circumstancial.... if you have a key player and a top team has picked up an injury or a team is pushing because they are in the latter stages of their cup you have a chance to get a good price everytime.
i dont think the week of the season is as influential as the time of day - (this is for run of the mill players that most teams wont set an alarm for to compete for) For the top 10% of players you can bet that there will be interest from a minimum of 2 teams and from what i've seen neither will ensure the other gets an amazing deal so from the sellers perspective its all good.