It could take you from 3 weeks to 6 weeks, depending on how many hours you are cooking.

A plan for what you can cook:
Tuna: 1 gives you 100xp
Lobster: 1 gives you 120 xp
Swordfish: 1 gives you 140xp
Monkfish: 1 gives you 150xp
Shark: 1 gives you 210xp

Cook Tuna until you get to about lvl 75 that way you can start cooking lobsters without burning them or burning less of them, than cook Lobsters until you get to level 84 so you can start cooking swordfish without burning them, around level 88 start cooking monkfish, and you can continue cooking monkfish until you get to level 99 or switch to sharks when you get to level 95.

It may take a while.

Best place to cook if you are a member is in the Rogue's Den, where you can thieve. There is a forever fire and a bank like 1 step from the fire. Most people who cook go here or cook at the range in Catherby next to the bank.

your best bet is going to goodle typing cooking calc and type in your name and it tells u exactly what u need to buy and how much you need to cook

You can burn lobster at 70 fo tuna till 90 and then lobster till 96 then go sworthfish till 99 you will probably wait about 80m and gain 65m