Does the time difference between Manila and Singapore change during the year?

No. Both cities keep the same local time all year.

When is the best time to call Singapore from Manila?

Between 09:00 and 17:00 in Manila, which is 09:00 to 17:00 in Singapore.

Manila and Singapore are on the same local time. This gap is the same all year — neither city shifts its clocks relative to the other.

Manila

Philippines

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Singapore

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A 9-to-5 day in each city overlaps for 8h. That is 09:00–17:00 in Manila, which is 09:00–17:00 in Singapore.

City	Time zone	UTC offset
Manila · Philippines	Asia/Manila	UTC+8
Singapore · Singapore	Asia/Singapore	UTC+8

What is the time difference between Manila and Singapore?: Manila and Singapore are on the same local time. This gap is the same all year — neither city shifts its clocks relative to the other.
Does the time difference between Manila and Singapore change during the year?: No. Both cities keep the same local time all year.
When is the best time to call Singapore from Manila?: Between 09:00 and 17:00 in Manila, which is 09:00 to 17:00 in Singapore.