Posting time is primarily controlled by the merchant, which has authorized the transaction but apparently not finalized it. I often see this type of delay if buying airline tickets, especially through an agency.

I suggest that you ask Chase for guidance on the amount that you can exceed the nominal credit limit on a VISA Signature account. Typically it is a small multiple of the limit (2X or 3X), but if your account is new it would be best to explain your anticipated transactions.