If you have the
Always send group/scene cleanup messages checkbox DISABLED (via
Interfaces->Insteon->Configure... menu item, then
Interface Options... button) no delay should be okay. If that option is enabled, then individual commands to all the modules in the scene/group have to be sent after the initial scene commands, so it gets more complicated. A delay shouldn't really be needed as Indigo waits before sending out commands but things get more complex when you have all of those commands being sent. Point being, I recommend having that option disabled.