The banks will not release the funds to the beneficiaries directly. They will be released to the Executor of the estate, who will then disperse the funds to the beneficiaries as per the terms of the Will. How long this takes, only the Executor and the bank can say.
When the Probate cert is issued, the Executor will contact the bank, produce the certificate of Probate, and make arrangements to have the funds of the deceased transferred into their Executor Account. The Executor will then write checks to the beneficiaries of the Will from this account.
If the Executors are a firm of lawyers, they may take their own sweet time doing this, depending on how fast/slow they are to deal with this sort of matter. If it is a private individual acting as Executor, it all depends on how motivated he/she is to wind all of this up.
If the bank is satisfied that everything is in order with the Probate cert and bank account in question (for example, there are no outstanding loans/mortgages attached to it, or someone else claiming joint ownership of it) they will probably release the funds pretty speedily. They have no reason not to. But overall, its the Executor who decides how fast things happen, not the bank.