Teams that haven't logged in for more than 6 weeks are converted to bots on early Monday morning (local time for the country). High value players are made free agents at that time, and given a random deadline (I think it something like 60 to 84 hours, or 72 to 96 hours). So players from New Zealand or Japan will tend to have deadlines a bit earlier than those from Europe, and those from the Americas will be somewhat later around Wednesday or Thursday.
If you notice the total number of teams shown when you log in, it always drops by several hundred on Mondays, and then grows throughout the week as new owners sign up.