You could go with a mapped key for PW: Shield.

Give it as many steps as you have Priests on your team.
And set the condition to not advance to the next step for however many seconds.

Whether it outputs a keybind to Warcraft, where you have the PW: Shield spell or macro...
Or if it uses an IS Boxer macro for the PW: Shield is up to you.

Withholding keystrokes is not considered botting.
As long as every action that happens in game, is a direct result of your input at the time the game receives the output (no delays or loops used... which you cannot achieve with IS Boxer anyway).

The whole 1s thing, is going to be based on your spam speed.
Blizzard has already removed the ability to use commas (do nothing on this press of the key, for this castsequence) as a timing mechanic.
The 1s, as Khat explained, is an attempt to /use the Helm Slot item... which since almost all helms don't have click effects acts as a timing mechanic.
It is part of the Blizzard system, so you're not going to receive account disciplinary action from using it... but it exactly duplicates a feature which Blizzard chose to remove, so you're definitely violating the spirit of the EULA/ToS when you use this kind of macro.
Also, since this exactly duplicates something that was removed, I can guarantee Blizzard will break this type of macro in the future.
But having IS Boxer withhold a keystroke isn't going to break or be removed.