In cell C1 use the formula =INT(B1-A1) to get the days. Then you have to get the remaining hours, which is the formula =MOD(B1-A1,INT(B1-A1)) and represents the remaining time. So in cell D2 enter the formula =HOUR(MOD(B1-A1,INT(B1-A1))). In cell E2 enter the formula =MINUTE(MOD(B1-A1,INT(B1-A1))).
You can opt out of Medicare Part B and in some situations you should opt out. Most people are automatically enrolled in Medicare Part A and Part B when they turn age 65. And most receive Part B at no charge. Medicare Part B is optional and you may not need the coverage if you have a group health plan.
With regard to whether Medicare requires you to keep your private insurance coverage for your husband, the answer is no. He has a right to his Medicare coverage regardless of what other insurance might be available to him. If he drops out of your private insurance coverage, Medicare will become his primary insurance. If you drop his private insurance coverage, he can get prescription drug coverage in either of two ways through Medicare. He could enroll in a Medicare Part C Medicare Advantage plan that includes drug coverage.