There is no fix delay, there is no protocol on how long a designer can do a job... this is insane.

first, you need YOURSELF to have a ETA... a date where the style have to be installed and perfect for your taste...

after that, you check for any designer that can do such job in such delay. usually, take a designer that will do it in half the time you have your ETA, so if there is changes to be made, you have the time to do it before your open that site.

NEVER pay before the job is done. if a designer/coder request to be paid before, it is because he wants to be sure you can pay.. this is stupid, because he can continue to use his work if you do not... so forget about the reasons... you can pay a upfront of 20 or 40%, but for a simple job, do after...

i sometimes had clients that were so stressed about their design that we were taking ages to make it perfect... i always charge for the extra work to be done... so they calm down on expectations... but i have a good reputation, so i'm not overbidding.

keep in mind to never take the first designer that comes to offer... evaluate the talent of others too... if someone have no portfolio, drop it right now... designers are proud of their works... they keep traces.