MATLAB does not offer an absolute time timer, only relative time timers. Your options are:
1) use Windows "at" or similar to command matlab be started to run a command, such as using the "batch" option. The timing is kept outside of MATLAB, but the program might take a minute to launch https://docs.microsoft.com/en-us/troubleshoot/windows-client/system-management-components/use-at-command-to-schedule-tasks
2) have a periodic timer() object that checks the current time and starts a file handle you have previously stored in a data object. Because the timer is likely to drift, you might not launch at exactly the time you want, but when you do start, the function will start immediately without having to wait for matlab to launch. The more often you schedule the timer, the more resources get used.
3) Use an adaptive scheduling of the timer, such as every 6 hours when it is not close to the launch time, but more and more frequently as the time approaches, paying attention to the difference between scheduled start and actual start to try to estimate drift and timer() overhead, with a goal of eventually starting the function as near as possible to the scheduled time. When you got close enough, you could launch slightly early and have the function pause() for just less than the time remaining before the scheduled time. You would only bother with this kind of trouble if it was important that the function start time was as close as possible to schedule.
