This is a story told over and over again for years and decades now. I've lived it from both sides.
You mention "change order" and talk about the product being finally "delivered" per a "deadline." This tells me you are using some form of the waterfall method. If I were you I would ask the team to shift to agile. They probably know how but are using waterfall because they think it's what you want.
Here are some big changes you should expect:
- No sign-off of specs, no change orders, no fixed "deadline" for the whole project
- They should deliver working software to you within 2-3 weeks and then every 1-2 weeks after that, if not continuously
- Your specs will be vague, short, and changeable with no formal change process
- Expect to be high engaged with your dev team -- every dev can reach you on IM or phone -- expect several calls per day
- Expect to personally review and jigger priorities often -- maybe once per week
These are simply the markers of the agile method, which is very mature and SOP in most quarters for a long time now. Beg pardon if I sound condescending and you are well aware of agile, but if you're not there's massive amounts of material about it on the Interwebs. IMO it matters little what flavor of agile you adopt: scrum vs kanban vs XP vs whatever. But any way you go you will have more satisfying outcomes that with a waterfall method.
What you lose with agile is a sense of certainly and control at the start of the project. You lose the liberty yo check out of the process and let the sausage be made by the experts absent ongoing guidance from you. What you gain is visibility, insight and meaningful control and, in the end, better software faster.