https://supportcommunity.milestonesys.com/s/question/0D5bH00000ZGNzKSAX/checkinpolicy-when-can-you-check-in-for-a-united-flight-everything-you-need-to-know?language=en_UShttps://supportcommunity.milestonesys.com/s/question/0D5bH00000ZGNzKSAX/checkinpolicy-when-can-you-check-in-for-a-united-flight-everything-you-need-to-know?language=en_UShttps://supportcommunity.milestonesys.com/s/question/0D5bH00000ZGNzKSAX/checkinpolicy-when-can-you-check-in-for-a-united-flight-everything-you-need-to-know?language=en_US