Do / Did you have to.................today?

Which is the best answer to :
a) Do you have to feed the ducks today?
b) Did you have to feed the ducks today?

thanks

It depends on whether you are asking near the start of the day (a) or near the end of the day (b).
a) asks whether you have to do this later in the day (after the present time).
b) asks whether you had to do this earlier in the day (before the present time).

Not too sure about this -

Surely this is asked within the current time frame.

I guess when take out " have to " the sentence can never in present simple.
Do you feed the ducks, today? but it makes sense when we say - Do you feed the ducks every day? " rather than today as Todays shows the past. But,
Did you feed the ducks todays ? is always correct.

Todays shows the past - typo here " Today shows…"

‘Do you have to feed the ducks today?’ is asking about an event which has not yet taken place, so if the person has to do so, it will be after the current time (at this very moment), regardless of whether it is 10 seconds, 10 minutes or 10 hours away.