What?
A very quick article to calculate the time between two timestamps and break it down into days, hours, minutes and seconds.

Why?
I've done this in lots of other systems but here's one in Zoho Deluge.

How?
We're going to make use of the .toLong() function applied to a datetime datatype variable which will return the Unix seconds. 
// the now time
v_NowTime  = zoho.currenttime;
//
// correction: I want to specify a from datetime
v_NowTime  = '2021-09-21 21:27:15';
//
// now specify a to datetime (we're doing a working day so we add 1 business day)
v_NextTime = zoho.currentdate.addBusinessDay(1).toString("yyyy-MM-dd ") + "12:00:00";
//
// convert to seconds
v_NowEpoch = v_NowTime.toLong();
v_NextEpoch = v_NextTime.toTime().toLong();
//
// calculate seconds in between
v_UnixSeconds = v_NextEpoch - v_NowEpoch;
//
// determine days
v_Days = floor(v_UnixSeconds / 1000 / 60 / 60 / 24);
info v_Days;
v_UnixSeconds = v_UnixSeconds - (v_Days * 1000 * 60 * 60 * 24);
//
// determine hours
v_Hours = floor(v_UnixSeconds / 1000 / 60 / 60);
info v_Hours;
v_UnixSeconds = v_UnixSeconds - (v_Hours * 1000 * 60 * 60);
//
// determine minutes
v_Minutes = floor(v_UnixSeconds / 1000 / 60);
info v_Minutes;
v_UnixSeconds = v_UnixSeconds - (v_Minutes * 1000 * 60);
//
// determine seconds remaining
v_Seconds = floor(v_UnixSeconds / 1000);
info v_Seconds;
//
v_DayGrammar = if(v_Days == 1, "DAY", "DAYS");
v_HourGrammar = if(v_Hours == 1, "HR", "HRS");
v_MinGrammar = if(v_Minutes == 1, "MIN", "MINS");
v_SecGrammar = if(v_Seconds == 1, "SEC", "SECS");
//
info v_Days + " " + v_DayGrammar + ", " + v_Hours + " " + v_HourGrammar + ", " + v_Minutes + " " + v_MinGrammar + ", " + v_Seconds + " " + v_SecGrammar ;
// yields: 0 DAYS, 23 HRS, 54 MINS, 11 SECS

Convert Total Minutes to Hours:Minutes
This is for other scenarios: 
v_TotalMinutes = 1100;
//
// determine hours 
v_Hours = floor(v_TotalMinutes / 60); 
info "Hours: " + v_Hours; 
v_Minutes = v_TotalMinutes - (v_Hours * 60); 
info "Minutes: " + v_TotalMinutes; 
//
// yields:
// Hours: 18
// Minutes: 20

Convert Total Seconds to Hours:Minutes
v_TotalMinutes = 66000;
//
// determine hours 
v_Hours = floor(v_TotalSeconds / 60 / 60);
info "Hours: " + v_Hours;
//
// determine minutes
v_RemainingSeconds = v_TotalSeconds - (v_Hours * 60 * 60);
v_Minutes = floor(v_RemainingSeconds / 60); 
info "Minutes: " + v_Minutes;
//
// yields:
// Hours: 18
// Minutes: 20