How much does the 30% increase in profits equal? In order to set your pricing; my advice is to meet with the client & map out the objective. You'll need to understand how big an impact you can really have & how you will help them achieve that benefit.
For example, if you're going to be able to move the needle from $1,000 to $1,300 per month, you've increased profits by 30%, but the business just won't be able to pay you very much. However, if you can go from $1MM/mo to $1.3MM/mo, that's a very different story. How long will that benefit last? Is it a permanent solution, or will the client only get a few months benefit before their competitors begin doing the same?
All of that said- the amount of time it will take to for either client could be very, very different.

Always charge based on creation of value; Never charge for a consultation; Always make sure you take the time up front to understand what you can do for the client; THEN (and only then) do you start to come up with a price quote.