hello hazel at the hill i just put the parsnips straight into the roasting tin,straight from the freezer,there is no set time limit to cooking them,look at the colour and give it a poke with the tip of the veggie knife,it depends on how well you like them done,we like them on the softer side,i do find that parsnips tend to take a lot longer to roast than the spudz,what i do for quickness when i do a mixed roots and squash roast is after chopping into chuncks is part cook in microwave until they are at the ready to roast stage,do a few at a time as each takes a different cooking time,in meantime,chop up onion and put it uncooked in the roasting tin,followed by the other part cooked ones,drizzle with olive oil and roast until it looks done and the aroma is mmmmm around the kitchen