Sweet potatoes are planted by slips usually early in the year. They grow vigorously so they need a lot of space and deep soft soil or the potatoes wont be very big. they will bloom near the end of summer and usually the potatoes are ready to harvest about 120 days after they are planted.
Where I am sweet potatoes are perennial so they don't die back, in colder places they will yellow and die back. Usually we just use a fork and lift out the tubers to check when they are ready. We leave the vines in place or replant slips where we have taken tubers out.
Happy gardening in Hawaii. Gardens are where people grow.