I have just withdrawn my prestaked ERD token, how long it will take till the token in my wallet ?

It is a two-step process. I assume that you just did the withdraw INTENT transaction. The unstaking period is 7 days, after 7 days you can repeat the process for the actual withdrawal.

With the first action you initiate the withdraw process (you stop receiving rewards), and with the one after the 7 day unbonding period passes you finalize the withdraw process.

A few minutes, it depends how much gas you give for this tx