For dollar cost averaging (monthly deposits), is there a particular day of the month which is better for purchasing than others?

For Banks and other financial service providers, they will have a fixed date that they will cash in your DCA deposit every month.

For example, DBS/POSB does it on the 15th of every month.

Overall, it doesn't really matter which day you purchase, as long as you consistently deposit every month on the same day.

I think the banks/financial institutions got a specific date where they will cash in your DCA monthly deposit.

E.g. 18th of every month for Poems https://www.poems.com.sg/rsp/#faq-sbp

You have to ensure that sufficient funds are available at least 6 business days before the Transaction Date (18th of every month or the next business day if 18th of the month lies on a non-market day).