Under Keypress.
/castsequence [target=pet,dead,group] Summon Imp; [nopet,nodead,group] Summon Imp
/castsequence [target=pet,dead,nogroup] Summon Voidwalker; [nopet,nodead,nogroup] Summon Voidwalker
/targetenemy [noharm][dead]
/petattack [pet,harm]
/cast [mod:shift, @cursor, nochanneling] Rain of Fire
/cast [mod:alt, @cursor, nochanneling] Summon Infernal
And it working smoothly for me, when i hold ALT down while marco is running, and placing the mouse over there i want throw it down 
Small gif video → Wow_yGr84JO2Ku - where you can it its working fine for me, i throw it after i started the macro