The idea of the Dragon Tales event is that only one chapter opens up each day (reset time) so if you started your timer on Tuesday it's like this:
Chapter 1 - Day 1 Tuesday (13.5 hours)
Chapter 2 - Day 2 Wednesday (24 hours)
Chapter 3 - Day 3 Thursday (24 hours)
Chapter 4 - Day 4 Friday (24 hours)
Chapter 5 - Day 5 Saturday (24 hours)
Chapter 6 - Day 6 Sunday (24 hours)
Chapter 7 - Day 7 Monday (24 hours)
So to answer your question, yes it seems quite pointless to speed up the first few chapters if you are not going to commit all the way. In my opinion, it is better to wait out the easier first half then speed up the latter chapters. It costs more to speed up the final chapters yes but it makes much more sense since it gives you more time to finish the battles which are much harder compared to planting and harvesting crops.