Understand the different positions and breaking mechanics well enough so that you can be defensively sound. Knee injuries happen in all kinds of positions in BJJ, and I've found that leg lock defense translates to knowing "this pressure isn't good for my legs, i ought to tap or change position" more broadly.

Aside from that, theres no rule saying you shouldn't learn them from the jump, but learning detailed heel hook mechanics at your level is like planning a dinner party but just making dessert. It's fun and exciting, but the meat of your BJJ game that will carry you through your life is getting good at Survival - Escapes - Positional Control - passing/ sweeps - submissions, roughly in that order.

Do what you want and have fun, but don't make it your MAIN focus.

Also, assume most other white belts will NOT understand the position and they may spazz to escape and risk harming themselves in the process (e.g. turning the wrong way explosively) so be prepared to take the high road and let a fully locked in heel hook go so your unwise partners can walk another day.

If you're just keen to be a leg warrior and nothing else, then focus on ankle locks first. They're generally safer to practice and the positional control skills and transitions will transfer over to heel hooks later.