All year, the same gap
Neither Singapore nor Tokyo changes its clocks, so the gap is the same on every date.
12:00 PM Wednesday 15 Jul in Singapore is 1:00 PM Wednesday 15 Jul in Tokyo (JST, 1 h ahead).
Why daylight saving conversions need a date explains skipped and repeated clock readings. The rules here come from the browser’s time zone data and can lag a government change.