How are you to know they're referring to a measurement of time without any context? 'Dara' means second every bit as much as 'soicind' means second.
The only relevant context is that this exercise is in the Dates and Time skill. Nevertheless, dara should also be accepted, as well as déach (“second” in the musical interval sense), taca (“second” in the duelling representative sense), and cúntóir (“second” in the boxing corner assistant sense).
I'm doing a general "Strengthen Skills" exercise, not the "Dates and Time" skill ,and the very first question was "Second". It accepted dara as the answer, but popped up "Dara is an ordinal number and is not appropriate here when we are referring to a measurement of time" in the black pop-up that is usually used to indicate a typo.
The “Strengthen Skills” area selects exercises from all of the skills; “Second” → Soicind is definitely in the Dates and Time skill. Dara is noted as being in lesson 3 of the Numbers skill, so there could well be a “Second” → Dara exercise in the Numbers skill. However, as long as “Second” is a single-word exercise, that particular black pop-up isn’t helpful, since “when we are referring to X” has no accompanying context — particularly when done through Strengthen Skills.
I thought they meant second as the the second day, etc. considering its time. It can apply to both so I'm wondering why they only accept it in relation to time on the clock?
No; dara is “second” in the ordinal number sense, and soicind is “second” in both the time interval sense and the angular measure sense.
I was also doing a "Strengthen skills" exercise and put "dara", before seeing the discussion, just to see if it would accept it. It did, but still popped up the warning message.
I have just checked the dictionary hints for "second" and it lists both "soicind" and "dara"!