I have done these before, not for United but another staffing company. They pay per visit usually $65 or $75. You can realistically perform 3-4 per day. The exam alone takes an hour if your fast (involve glucose check, urine dipstick, monofilament test, vitals, eye exam, test of all cranial nerves, it's extremely comprehensive, review of all meds and teaching, checking drug interactions, etc). You must also call the patients the night before to tell them your coming. leave messages, call back, it gets time consuming. The paperwork alone is 12 or more pages of very detailed stuff so the company can get paid for everything you do.
In the end it was not worth it since time spent with the patient averaged 1.5hrs (these are elders with many, many, many conditions, questions galore and lonly on top if it so they want you stay). Time spent driving at least half hour between locations. The sad part is how much we are paid. The insurance company bills about $800 for a visit like that, we get $75? I figured after my time spent I ended up making about $20/hr. No thanks!! I did it for less than a week as soon as I saw the reality of it.