I had this issue before too. I found by going to my computer manufacture website (HP.com in my case), downloading and installing the latest BIOS released for your machine it can fix the computer slow boot. This could be temporary or permanent, don't know at the moment. When I turned it on this morning at booted like before the update, in under a minute.
By the Way: When I went to my product support page at asked if i was running Windows 8 or 8.1. CHOOSE WINDOWS 8 because your get the BIOS last released for it, don't install the one under WINDOWS 8.1 if such an option is available, as your computer will have downloaded that BIOS already and so obviously it didn't work., then Patch and restart.
It fixed my issue, hopefully it will work on others.