Double Boot Help

[D4550]

For the life of me I can't seem to figure out why my system is double booting.  Sometimes it will boot straight into windows most of the time it goes to the bios splash screen then goes to black for roughly 30 seconds and then goes back to the bios splash screen before booting to windows.  Its not a major problem but it changes boot times from five seconds to about a minute or more.  Specs below.  Mobo flashed to newest bios version.

 

Mobo:  Asus Prime Z370-A

CPU: i7-8700k

RAM: 32gb Corsair Vengeance LPX 4x8gb DDR4 3000 15-17-17-35

GPU: MSI 1080ti Duke

Boot Drive: Samsung Evo 250gb 

Storage: Seagate BarraCuda 2TB and 500gb Samsung 970 Evo 

PSU: Corsair RM750X