Interval Menu not accessable

Hello everyone. I tried searching for this issue first, but without finding a clear answer I'm looking to you for help.

I'm new to photography, purchased a D5100 and am currently obsessed with timelapses. While I'm still learning all the functionality, I'm noticing -quite frequently- that the interval option is greyed out in the menu. I've tried various modes (M, A, S, P), but it seems randomly turning off the camera and back on is the only way to activate this menu option. I'm sure there is some repeatable steps to get to this point, yet I've not found them.

Can anyone here point me in the right direction in solving this?

Thank you.

Does this tutorial help?

How to Shoot a Time Lapse With a Nikon D5100

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In general, when something is grayed out, it is because that feature cannot be used with another feature that is already set. So try to think of what you have set that might not be an 'everyday' setting. I don't have a d5100 to play with, but I know on my d7100, if the self timer is selected, the interval settings are grayed out. So think of what might be set or just reset your shooting and custom settings menus. The d5100 manual says bracketing, multiple exposure and hdr cannot be used with interval shooting, but I don't know if having those set will gray out the interval menu.

1. Be sure that the date and time are set.
2. It will be grayed out if you are in live view.

Also if you have HDR and Bracketing enabled.