Thanks for the replies!

Okay, so it's still not working. Here are the 3 different macros I just tried:

/ac "Bio" <t> <wait.3>
/ac "Aero" <t> <wait.3>

/ac "Bio" <t>
/wait 3s
/ac "Aero" <t>

/ac "Bio" <t>
/wait 3
/ac "Aero" <t>

This is really grinding my gears!