Best time to call
São Paulo is 12 hours behind Osaka. Here are the call windows that respect both your day in Osaka (Japan) and theirs in São Paulo (Brazil), plus the daylight saving and holiday traps to watch.
9 AM Osaka
= 9 PM São Paulo
9 AM in Osaka = 9 PM in São Paulo, comfortable for you but outside their working day, so agree it in advance.
10 AM Osaka
= 10 PM São Paulo
10 AM in Osaka = 10 PM in São Paulo, comfortable for you but outside their working day, so agree it in advance.
9 PM Osaka
= 9 AM São Paulo
9 PM in Osaka = 9 AM in São Paulo, inside their hours but early or late for you, so it is your sacrifice to make.
Watch out for these
Both cities are loaded with Osaka as the anchor. Adjust the day or hours to see the overlap shift, including around daylight saving transitions.
Sorted by participants in business hours
Green = inside 9:00–17:00
São Paulo is 12 hours behind Osaka. From your desk in Osaka, that means your afternoon is still their morning, and the window where both teams are at their desks is narrower than it looks. The cleanest single slot is 9 AM your time, which lands at 9 PM in São Paulo.
With a gap this wide, there is almost no natural overlap between a 9-to-5 in Osaka and a 9-to-5 in São Paulo. One side has to stretch. The honest move is to decide in advance whose comfort you are trading away, then rotate it so the same team is not always taking the early or late call. Do not pretend a painless slot exists; it usually does not at this distance.
The recommended slots above are computed against today's offset, which is the safe default. The trap is the twice-a-year daylight saving changeover: Osaka and São Paulo do not necessarily move their clocks on the same weekend, so for a few weeks each spring and autumn the gap can shift by an hour and every recurring invite quietly misfires. If your call is near a transition date, confirm the exact wall-clock time on both ends rather than trusting the difference.
On these dates both Japan and Brazil are likely off, so do not schedule.