Hi, newbie here. I purchased SIA stocks (cash upfront) on 4 May, but cdp account shows settlement date on 6 May. I suppose ex-right starts on 6 May but am I entitled to the rights?

Yes. You bought the shares on 4th May means you qualify for the rights.

Ex rights depends on PURCHASE DATE. Not settlement date.

If you look at the details, you will see something called the RECORD DATE. Which is afew days AFTER ex rights. By that time, the settlement will have been done and RECORDED