When asked if the ceasefire in Hudaydah province starts midnight Monday, the UN official, who requested anonymity, said, "it is true."
The announcement of the ceasefire date follows Yemen's warring sides clinching a deal in Sweden Thursday, under which an "immediate ceasefire" was to be implemented in Hudaydah.
The UN source told AFP the delay until 2100 GMT Monday was necessary for "operational reasons."
Residents in Hudaydah and the surrounding areas have reported fierce airstrikes in recent days, as clashes continued between Saudi-backed militants and Yemeni troops.