Here's a list of the service centers that I have been to and can confirm it's location as well as operating hours.
BSY Home Appliances Pte. Ltd. (Bosch Home Appliances)
Block 4012, Ang Mo Kio Avenue 10, #01-01
Techplace I Singapore 569628
Phone number: Tel: ( 65) 6751 5000*
URL: https://www.bosch-home.com.sg/service.html and https://www.bosch-home.com.sg/Default.aspx?SiteMapId=383778
Operating hours: Monday to Friday 8:30am - 5:30pm
*This number is a call center that is not located at the service center - Note: there is no publicly available phone number at the direct service center - I have asked them directly
This was a confusing service center for me to find in the first place, as there are a few Toyomi entities in Singapore that are not related to the appliances arm. I called them up (most speak Japanese-English) but in the end I managed to find them. This is why I decided to post these details, so you can find this place easily as well.
Address: National Electrical Traders
459 - 461 Geylang Road
Phone number: (65) 6748-5845 (5 lines)
Monday to Friday 9:30 am to 6:00 pm,
Saturday 9:30 am to 5:00 pm,
Closed on Sundays and Public Holidays.