It does only need as much time, as it needs to send the intent out - a short thought is all that is needed - so few seconds. But, if you are in a lucid dream, the one you called might not be able to enter - your subconscious/higher self protects you that way.
Yet, you do not need to be in OBE nor lucid dreaming to call helpers and work together with them.

So, yes, it is much more simpler than you think.