Yes it is rational. Mainly we spend time n things that bring us some sort of benefit, in this case profit. And spending time on earning bitcoins for profits or money is the most rational choice. Remember the saying "Time is money",and so is bitcoin.
Wasting time will if no benefit is realized from the time input you have invested in bitcoin. But all in all. If one understands bitcoin, that person will never waste time if its invested in bitcoin.