Ultherapy is skin tightening. Weight loss if excessive can leave you with extra skin - it is not likely, with your planned 10 pound weight loss plans, that you will have more loose skin because the fat is gone. The skin tightening will be as effective before or after weight loss. Read the Ultherapy book our group has published on the link below.
Considering the amount of weight you plan on losing, I do not feel this will present a problem. Also at your age, I would expect your collagen to respond well and that you would have a good result.
For modest changes in weight such as those you describe, the timing of noninvasive skin tightening is not important. For patients who are planning to undergo massive weight loss through surgery or other dramatic measures, noninvasive skin tightening may or may not be an option. In these situations is best to wait until the weight loss is complete before deciding which facial rejuvenation procedures would be best.