When you say you have surgery July 7th and want information about VEDs, does this mean you haven't used one before? If so, don't worry, I don't think it's a disaster. You've got 46 days until surgery so use them often. The reasons why they allow the surgeon to place a longer implant seem very reasonable and described in some the sources I link below.
I think of it this way - if you were born with a 7" dick but as you aged it whittled down due to fewer erections and worse blood flow and etc etc like all men's dicks do. Now your best measurements might be at 5.5". Using a VED provides treatment for the fibrosis that scared down your dick. To place the implant when you're asleep the surgeon uses a device to basically measure your stretched flaccid - if he did that on your 5.5" dick that had no treatment, it probably stretches only 5.5".
If you never have used a VED and care about this greatly, I think it's worth considering pushing your appointment back a few months, but surely that's not necessary and ask others here/doctors.
All the medical reasons why VEDs help with size before implant surgery and also after are explained in the first two sources here. And the second two sources provide medical reasons why these devices have been proven effective at treating ED for at least 40 years:
viewtopic.php?f=6&t=18561&p=169469#p169469 And since anecdotal evidence can sometimes be even more meaningful, here's how it helped with another member here:
viewtopic.php?t=19159&start=10Also I have been curious about something with Rider - he used a VED for 17 months and eventually he seemed to literally regain all his size even before implant since his injection sizes were same as VED size. Which is great, but for others to know 17 months surely isn't required. I wonder if after 2 months of VED use your stretched flaccid works great enough when the surgeon does it your VED is all you needed. I don't think I've really come across anything about how long of a timeframe is best to use them before implant.