Hi Kitty,
You will find the majority of stallholders in Patong wont open until at least 10 but a few may open up earlier. It wont start getting busy around the shopping areas until mid afternoon so you can still get a leisurely 4 hour shop in before lunch. Once you are there and become accustomed to the pace of Thailand you will realise that 10 is early enough as even if you are an early riser and up at 6, you will need time for a morning swim/walk/run and then at least an hour if not 2 for the buffet breakfast which is a great spot to do some people watching whilst reflecting on the previous day and planning the day ahead. Only then will you sufficiently recovered from your hangover from the night before to successfully tackle the subtle art of bartering for a deal with the local street traders.
I would recommend that you have a look in the larger shops first like the Jung Ceylon centre to get a guage of pricing before making too many street purchases as they tend to prey on the uninitiated in Patong. And do save a large chunk of you shopping budget for Bangkok as it tends to be alot cheaper there. If you want a good deal in Patong be prepared to walk away before getting their best price and dont make an offer if you are not intending to buy as they will get upset with you. As a geral rule of thumb,my wife, if offered a price of 500baht on an item, will say that she saw the same thing for 150baht in Bangkok and after some good natured banter,will settle on about half the original quote. If you do this with a big smile on your face you will get the best results.

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I love Thailand this much