When you want to know how long something is, there are a lot of different units that you can use to measure it. For example, a second is a very short amount of time, but an hour is a much longer period of time. We use minutes to measure how long we spend on activities like brushing our teeth or taking a shower, and hours to measure the length of a school or work day.
How to convert seconds to a full time or duration expressed in HH:MM:SS is simple, just divide by 60. The number to the left of the decimal point is the number of whole hours, and the number to the right is the number of partial hours. This means that 90 seconds is equal to 1.5 hours.
The most common way to convert between seconds, minutes, and hours is to simply multiply by 60. This is also how you can calculate how many seconds are in an hour — simply subtract the total number of seconds from the total number of minutes and then divide by 60 to get the number of minutes that passed since the beginning of the minute.
Occasionally, a minute may have 61 seconds, but this is only added to the clocks that are set to civil time and used in atomic clocks, as they require a very precise definition of the second. However, most watches and clocks do not keep track of leap seconds and use the more conventional definition of a second: 1/86,400 of a mean solar day.