According to the Gamepedia wiki, spectral arrows are supposed to impart the Glowing effect for 10 seconds. When I use them, it actually does it for about 17 seconds. So I did some testing, and if you give a player or other entity the Glowing effect, it lasts much longer than specified. I couldn't discern a pattern, but in my tests, using "/effect @p minecraft:glowing 5 0" gave me glowing for a bit less than 15 seconds instead of 5. Doing the same using 10 instead, it gave me the effect for 17 or so seconds instead of 10. The weird part is that the HUD next to my inventory shows the proper amount of time, but when it reaches 0, the effect stays applied for much longer before the HUD even disappears.

To reproduce:

1) Use /effect @p minecraft:glowing 10 0 to apply the Glowing effect for apparently 10 seconds.

2) Open your inventory and watch the effects tab. When Glowing reaches 0, you'll see the effect remains almost twice as long anyway.