1. A method in a data processing system for maintaining a best-case demand redispatch of an instruction, the method comprising: responsive to a demand miss, sending a fetch request to a next level cache in a memory hierarchy; examining a cache line of the demand miss to identify a critical sector of the cache line; generating a best-case data return arrival time by determining a fastest time the next level cache is able to return the critical sector of the cache line; and sending a speculative warning to a dispatch unit to coincide with the best-case data return arrival time, wherein the speculative warning prepares the dispatch unit to resend the instruction for execution as data in the next level cache becomes available to a processor core.