Designate for Assignment only removes a player from your 40-man and passes him through waivers to do so. Since there is no DFA list or roster section, there is no 10 days. When you click and select remove from 40-man, you are designating for assignment and the player is immediately passed through waivers and either sent to AAA if he is on the 25-man roster or remains where ever he was when you DFA'd him if he is not claimed off waivers. If he is claimed off waivers a message box will immediately pop up and tell you that such and such a team has claimed him and he will be gone from your roster.