I called Hermes customer service in Paris (number is on the French version of the Hermes website; it is the main customer service for the company, not the customer service for the website). If you want to put your mind at ease I suggest you give them a call.
I will go on first day only. They don't do deeper price reductions as the sale goes on and best selection is on the first day. However lines are worst on the first day. If you want to be amongst the first in the sale I suggest lining up at the Palais des Congress by 6 AM on the Wednesday (that is when I will get in line). There are limits on what you can buy, for example at the last sale it was a maximum of 10 of the 90 cm scarves, 10 neckties and 3 or the other sizes of women's scarves. You might be able to get around the limits by paying for everything, leaving and then standing in line all over again (not sure if they allow people to do that or not).
You also should be prepared for a couple of further lines within the sale: there is one queue for the 90 cm women's scarves, a separate queue for other women's scarves and a third queue for jewellery (January)/belts (June). Other things (RTW, neckties, homewares, shoes) don't have separate queues.
I have been to the sale twice and both days got in when the sale opened and finished between 11 AM and noon. Depends on your priorities but suggest you do one of the scarf queues first to get that out of the way and leave the RTW and other items until last. They only give you 20 minutes or so to make your scarf selections, then they hustle you out and let the next group choose. Also the jewellery/belt queue can move pretty slowly so allow time for that if you are interested in those things.
Also don't expect to find any bags at the sale--I heard that years ago they used to have them in but the two times I have been there were no bags whatsoever. All of the merchandise is from at least two years ago so don't expect to see things from the last few seasons. That said, I have found tons of stuff both times.
The queue is upstairs in the Palais des Congres and is sheltered from the elements. I will be in the queue from 6 AM, you are very welcome to join me. There are many hotels near the Palais des Congres, I suggest staying in one near there if you are only coming for the sale. Hope that helps!
