Hello shack-
In order to have your request taken seriously, you must be able to show how you have been delayed, through no fault of your company, and why a time extension is warranted.
Provided you have this documentation, you should be able to make a case for a time extension. Take the time to review all of the facts, and determine how this has impacted your work. Was the foundation poured later than shown on the schedule? Was the permit process delayed due to engineered drawings failing their review with the AHJ? Did another trade fail to perform their work in a timely fashion, thus causing you to be delayed? Show how these impacts prevented you from performing your work in a timely fashion.
You might want to gently mention that there are possible financial ramifications as well. I stress mention. This gets the GC / Owner thinking and a possible claim / legal battle / lien. Be polite, do not take things to a personal level, and make requests not demands. Ask them for their thoughts on how to get the project completed without causing delays or damages to either party.
I hope these ideas help.