I have a Samsung 840 EVO booting Windows 7 Ultimate 64-bit, and there are times when it would just take so long to get past the Welcome screen. I notice that running Samsung Magician and doing an OS Optimization fixes things (even if I go to Power Options and re-select the Balanced power profile .. Samsung creates a new profile called Samsung High Performance or something... I don't trust it to save power). Also, if I do a reformat and reinstallation of the OS and everything it fixes the problem. Given these, I don't think it's an issue with the SSD itself, but with the OS. Perhaps it's doing some cleaning up or whatever during boot time.
NEC V20 > AMD Am386DX-40 > AMD Am486DX2-66 > Intel Pentium-200 > Cyrix 6x86MX-PR233 > AMD K6-2/450 > AMD Athlon 800 > Intel Pentium 4 2.8C > AMD Athlon 64 X2 4800 > AMD Phenom II X3 720 > AMD FX-8350 > RYZEN?