I've found the best way to manage enemies is to have all of them in a separate layout that never gets loaded. Then through events you can spawn them into your current layout at whatever position you want.
For attack patterns, try giving each enemy type a PV "pattern" that controls how it will move:
if pattern = 0
-> fly straight code
if pattern = 1
-> wave movement code
etc
To have a formation, when spawning in enemies use the "repeat" condition and just offset the x or y positon and set their pattern to the same number.
As for the time implementation, couldn't you use the "compare time" condition?