One of the following is correct, but which one?

A) You Special Summon Helios only when the card is first flipped face-up.
B) You Special Summon one Helios any time you want since Macro is continuous.
C) You Special Summon any number of Helios's any time you want since Macro is continuous.
D) Rulings aren't out yet.
E) None of the above.

The only ruling I know of right now is...(from GONDORA and DMComet)

EOJ-JP057 Macrocosmos
- This card can be activate even if you don't special summon a [Helios] from your hand/deck


So I would say...

A.) You choose whether or not to Special Summon Helios when it's activated

You can choose when to activate the effect of the card of summoning. If you special summon after later on, the actualy card can not be negated by Counter Cards like 7 Tools, Solemn. However, cards can still respond to the summoning.

Actually...Helios' summoning occurs when the card activates.

You flip it, decide whether or not to Special Summon it and then something can be chained in response. Much like the way Call of the Haunted is done really.