Damn… I’m sorry, man, that really sucks 
Try not to get too discouraged… it’s easier to get to level 400 than ever and while the box saves you some time you can probably do it in 2-3 evenings (even less if it’s your first character and you haven’t opened the F5 rewards yet). Again it’s a pain in the ass to miss out but we can still get some decent stuff on weekdays and weekends from this Arbor day event 
Yea i got one at lvl 436 atm, but was a shame i missed out on these two last attendance things since i looked forward for the charslot and lvl boost for an alt. And the anvils. Was logged in all day on sunday so never logged on to character screen again to see the mail. And on sunday it said on the mail that i would last untill april the 20th i belive. So i didnt claim it right then to save some days from the 14 day lasting period. DOH! =D