According to this map, Singapore is in the "wrong" time zone: Since she's westward of VN, the time zone should be one hour lag to SG's.
The short answer I found in the net is "Sometime in 1981, Malaysia declared that West / Peninsular Malaysia would move their clocks ahead by 30 min to match the time in use in East Malaysia (8 hrs ahead of GMT). This meant that Singapore would be in a rather awkward position in time if she didn't follow suit, especially with the amount of traffic and trade across the causeway." (https://www.quora.com/Why-do-Peninsular-Malaysia-and-Singap…)
East Malay is in the same time zone as Perth.
Perth is eastward of VN, so she leads one hour.
