the information you enter here runs only on your browser on your machine, no data is transmitted to a server unless you use bookmark URL button, then it submits to same page (nothing active on server side) and builds a URL.
These are time/date calculators. because of the way relative time works, I have included a special time format I have named DTime, which includes days, hours (24-hour time format), minutes, seconds, and milliseconds. everything here has millisecond resolution. you must fill out all fields at least with a 0 for it to work except for gregorian day and month,which area minimum of 1, and all time is 24-hour time format (hours are 0..23).
Part of Windows CUA (Common User Access) means you can hit the Tab key (or shift-Tab to go backwards) to move/switch between fields/controls. this also selects what's in it automatically for replacement.
math can be used in any input. math.js is used, so if you want to get technical, you can look up the documentation on that.
DTime = milliseconds + (seconds*1000) + (minutes * 1000 * 60) + (hours * 1000 * 60 * 60) + (days * 1000 * 60 * 60 * 24)