Originally Posted by
Often1
DL requires that OP be at the xDTW gate no later than T-45, so 40 mins. is 5 minutes too little time even if OP's inbound is on-time and he magically teleports from his inbound seat to his departure gates.
In particular, at T-45, his seat is subject to cancellation and, if the flight is in danger of an oversell, DL can offload OP and give his seat to a SB pax.
This is not a legal connection, leading me to believe that OP is either on two tickets or that there has been a schedule change since he booked. If the former, he needs to change the first segment (and it there's a fee, eat it). If the latter, DL will rebook without fee.
IIRC the rule for international is that passengers must be on board at T - 30. I've never heard of the 45 minutes rule you state for DL.