Yep. That's how these suckers operate. DHL's actually one of the better services out there.. based on my own experience.. And they're apparently not even legally binded to deliver by any time, whatsoever... as their TOS says in there somewhere that they only AIM to deliver by a certain time... but may well, in fact, deliver ANY time they see fit... so long as they deliver, they're not breaching any conditions of their contract. Very convenient 4 them.
My own experience says that there's a problem of some sort out there with every other deliver I get (that, inevitably, causes a delay). E.g. the last package I got from an international delivery courier service (UK, won't name which service it was) was delayed from a scheduled "Friday"-due delivery to Wednesday, because of things like them leaving the package out of the delivery track by mistake, running late on their scheduled deliveries (they only deliver from hour to our, i.e. as soon as it hits 6pm, they're off back to their hub), "no one was home" issues (BS in many cases)... Stuff like that... So much for paying the extra $$ for their promised 'fast' worldwide service.. And, in my view, their quality of service only seems to get worse with time.
