I've been having the same exact problem as well. However, what some of you didn't notice yet is that when you get the slow speeds you also get packet loss, high pings, and slow videos. I've had this problem for the past years and Verizon doesn't want to fix it because they're cheaping on. All they have to do is probably upgrade their servers. What is happing is that when there's a lot of traffic Verizon's servers can't handle it so they start having problems. I have my forum post here, you can take a look. Also, the problem is not coming from your end, it's from Verizons end. I'm 100% sure.
I was lead down the path of a possible duplex mismatch, but either Verizon is either purposefully throttling internet, or they have a problem they are either unwilling or unable to resolve.
Verizons network can't handle the traffic at peak times, they need to upgrade their network to fix this issue. BUT, they're too cheap to do so. I've had 2 Verizon technicians, and a level 3 network team technician tell me that they know about the problem but they doubt they'll upgrade their network anytime soon. Consider switching to another provider at this time.
I've had this problem but just in the last couple days (since 3-7-2015, DC/VA area). Packet loss has gotten so high that basic websites have difficulty loading and good luck with video. It gets worse in the 7-11 pm period but each day since Saturday the 7th it's been progressively worse at all hours. So while peak EST times are really bad, even my mornings are starting to suffer now.
Starting to seriously consider another ISP except if my local options are Comcast and worse... well. It's great being a local monopoly, isn't it?
I'm in the DC/NOVA area as well and I'm just noticing this today. On 75/75 and am getting ~3/65, improving as it gets later, past midnight. I've had Fios for a few if not several years now and never noticed this before. Spent the last several hours trying to troubleshoot on my own and then with Verizon on the phone (worthless). Until I read this thread, I thought it was a problem with my router or something else physical -- splittlers, coax, line into my house. Even setup an appointment for a tech to come out this week and look at it. Now I'm starting to think otherwise.
I am experiencing the same issues in Rhode Island. I went through the normal troubleshooting, but the results are identical to everyone else here. Slow downloads and near normal uploads. Very annoying.
Here is my most recent Speedtest result for my 50/50 FIOS line: