DateInterval How to reduce the time

DateInterval How to reduce time
For example, this code is to get the current time plus 3 hours, then how to get a reduction of 3 hours?

PHP Code

  
  (New \datetime (' Now '))->add (New \dateinterval (' pt3h '))

------Solution--------------------
Dateinterval::format ()-Formats the interval
Datetime::add ()-Adds an amount of days, months, years, hours, minutes and seconds to a DateTime object
Datetime::sub ()-Subtracts an amount of days, months, years, hours, minutes and seconds from a DateTime object

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