About the same time the basement floor is poured, temporary power needs to be installed on the site. The contractors before this point usually have little or no need for power, but after the foundation is in, the framers (and others) will need it. The temporary power pole often is hooked up by your electrician - and may included in his bid for your project (you will want to ask to be sure). Mark (our builder) prefers to hire a separate company that does nothing but hook up temporary power poles - mostly because they are more flexible in scheduling than the electrician.
Setting up the power pole only takes an hour or two - but the final hookup is done when the power company comes to the site and sets the meter in the power pole which turns the system on. Make sure make a call to the power company plenty early - one week after having the pole set, we still did not have a meter (and hence no power).
Our neighbor across the street (who is building a house) was very gracious and allowed us to tap into his power. If this was not available, the workers on the site would have been forced to use generators, and would certainly charge additional for this.