1. We'll see you in the morning on Tuesday, July 14.
2. We'll see you on Tuesday morning, July 14.
[Are both okay?]
3. On Christmas, we share love with our family and friends.
4. At Christmas, we share love with our family and friends.
5. On Christmas eve, we share love with our family and friends.
[Do we have to use on or at? Are both okay?]
1 and 2 are OK. It's unusual to include the date, though.
1 and 3 are OK. I'm not sure if "at" is used for this purpose in British English or not, but it isn't in the US.