No. Plotting can be done entirely offline and needs nothing from the blockchain to complete. The only time you have to be online and synced is when you're farming so that you receive new challenges for the next blocks and transactions to include in a transaction block if you're lucky enough to win one of them and get the transaction fees. Note that one farmer winning is independent of other farmers winning at the same time. All farmers can "win" at nearly the same time. That is why sometimes there are 10 blocks in one minute, and sometimes there is only 1 block per minute, etc.