Pumpkins are mature when the stems connecting the pumpkin to the vine begin to shrivel. Pumpkins can be harvested whenever they are a deep, solid color (orange for most varieties) and the pumpkin rind is hard. If the pumpkin vines remain healthy, harvest in late September or early October, before heavy frosts.
Harvest pumpkins before the first hard frost. Cut pumpkins from the vines carefully, using pruning shears or a sharp knife and leave 3" to 4" of stem attached. Snapping the stems from the vines results in many broken or missing "handles." Pumpkins without stems usually do not keep well. Wear gloves when harvesting pumpkins because many varieties have sharp prickles on their stems.
In short, leave them on the vine as long as possible, as long as the vine is healthy. They'll keep longer. If you were going to try for larger fruit, you should have picked off all the flowers but one before they set fruit, then the energy would have gone into the one or two...but I don't think removing the pumpkins now would do much to the remaining pumpkins. If there are more coming, I wonder if they'll ripen by the time the vine starts dying, anyway. Don't sacrifice the ones you have to try to get more.
