How to be smart with contracts?

So, if you offer a player a new contract after he is Wanted, clubs can't offer transfers for him for X amount of time.

Like I want to sign a player, but he just signed a contract, how long until I can make an offer?

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Similarly if I want to keep a player, who is wanted by several clubs, then I figured I'd have to offer them new contracts before transfer windows. But how long does that window last where they can't approach him?