Transforma horas com PM em horas normais.

transformPMHourToNormal.js

const periods = [ `am`, `pm` ]
const getTimeWitoutPeriod = ( time ) => time.split( /(am|pm)/ )[0]
const getHoursAndMinutes = ( time ) => time.split( `:` )
const testIfHourIs00 = ( time ) => time.startsWith( `00:` )
const timePuls12Hours = ( h, m ) => parseInt( h ) + 12 + `:${m}`
const removingTimeFrom = ( time ) => time.split(/[0-9]/)
const timeIfIsIn = ( periods ) => ( time ) => 
  periods.includes( time )

const getOnlyThePeriod = ( time ) => 
  time.filter( timeIfIsIn( periods ) )[0].toLowerCase()

const getPeriodFrom = ( hour ) =>
  getOnlyThePeriod( removingTimeFrom( hour ) )

const getMorningTime = ( hour ) => 
  transformAMToNormal( getTimeWitoutPeriod( hour ) )

const getEveningTime = ( hour ) => 
  transformPMToNormal( getTimeWitoutPeriod( hour ) )

const transformAMToNormal = ( time ) => 
  ( testIfHourIs00( time ) ) 
    ? timePuls12Hours( ...getHoursAndMinutes( time ) )
    : time

const transformPMToNormal = ( time ) => 
  ( testIfHourIs00( time ) ) 
    ? time
    : timePuls12Hours( ...getHoursAndMinutes( time ) )

const transform = ( hour ) =>
  ( getPeriodFrom( hour ) === `am` )
    ? getMorningTime( hour )
    : getEveningTime( hour )

const hourPM = `05:01pm`
console.log( `Transforme ${hourPM}: `, transform( hourPM ) )
const hourPM2 = `00:01pm`
console.log( `Transforme ${hourPM2}: `, transform( hourPM2 ) )

const hourAM = `00:01am`
console.log( `Transforme ${hourAM}: `, transform( hourAM ) )
const hourAM1 = `05:01am`
console.log( `Transforme ${hourAM1}: `, transform( hourAM1 ) )

ui :)