Once you make hash browns the uncooked has browns will last for up to 5 days in the refrigerator before they start going bad and growing mold.
Cooked hash browns will last just about as long as the uncooked hash browns and cooked hash browns should last 5 to 7 days in the refrigerator.
If you want to keep the uncooked hash browns longer than 5 days you should place the hash browns in the freezer and when frozen the uncooked hash browns will last for 6 months to a year.
Cooked hash browns will last as long as a year when frozen.
You can prepare the hash browns and then refrigerate them for 5 days and then cook them when ready or freeze the extra prepared uncooked hash browns and then cook them as long as a year later.
However for the freshest hash browns it's best to eat them within a few days of making them or make the hash browns and then cook them right away.