Easier than you think.
First, what is the current time?
CurrentTime = now
CurrentTime =
738645.50979622
That might not seem terribly helpful. However, datestr will help a lot.
datestr(CurrentTime)
ans = '04-May-2022 12:14:06'
You want to see an offset of 6 hours before that time. That is 1/4 of a day.
datestr(CurrentTime - 1/4)
ans = '04-May-2022 06:14:06'
So we are getting there. But of course, it is not exactly in the format you wish to see. First we will fix the date part, and you want that in the form of Year, Month, Day. The integer part of the time reported by now is the date. For example, we can do this:
datestr(fix(CurrentTime),'yyyy-mm-dd')
And that gives you the date in a format as you desire. You can format the time part similarly.
datestr(CurrentTime - fix(CurrentTime),'HH:MM:SS')
And then you wanted a spare T and Z in there for some reason. So we might write a little helper function like this:
mytimeformat = @(CT) [datestr(CT,'yyyy-mm-dd'),'T',datestr(CT - fix(CT),'HH:MM:SS'),'Z'];
mytimeformat(CurrentTime)
ans = '2022-05-04T12:14:06Z'
As you can see, that formats a time and date in the way you want it, specifically with the extra characters in there. The second time you wanted to see was 6 hours before that.
mytimeformat(CurrentTime - 1/4)
ans = '2022-05-04T06:14:06Z'
I'm sure there re other ways to do this, but the point is, when you have a difficult problem to solve in MATLAB, start from something you can find. Then work with it. Perhaps you can massage that result into something close to what you need. Then keep on working at it. In the end, you will see it was easier than you thought all along.
