An infected tick must be attached for 24 to 48 hours to transmit Lyme disease (and at least 12 to 24 hours to transmit anaplasmosis, another serious tick-borne disease). Lyme disease is unfortunately a fairly common canine disease. Symptoms can include fever, reduced energy, and lameness.
D-day(n.) (Mil.) the day designated for the beginning of a planned attack by a military force; in communications the day is often otherwise unspecified for security reasons; as, the day before D-day the troops will move into position.
In short, the D in D-Day comes from the word Day as does H-Hour comes from Hour. Military planners use D-Day and H-Hour in every operation to designate THE Day and Hour that an operation is scheduled to 'kick off' or start. Instead of saying D+0, we just use D-Day because it is easier to say and makes more sense. Operation Torch, Operation Avalanche and all operations had a D-Day and H-Hour.