The reason for this sort of thing on epay is, I think, that the computer is programmed to calculate the e.t.a. from the purchase date, but be generous to the postal/delivery system. I have occasionally asked for delayed delivery if, for instance, delivery might be when we are away from home. Epay often reminds one to pay for an item even though arrangements have already been made for personal collection.
Items from China often arrive far earlier than the estimate. A combination of carrier (air or surface) and non-delay with customs, etc. As usual, 'bull excrement in bull excrement out' applies to computer programming.