5.1.5. VAVAILABILITY
DTSTARTandDTENDif specifiedMUSTbe date-time values.DTSTART MAYappear once and signifies start of the busy period.Only one of
DTENDorDURATION MAYappear and signify the end of the busy period.If
DURATIONdoes appear in aVAVAILABILITY, thenDTSTART MUSTalso appear in the sameVAVAILABILITY.