Not sure about the connection times - but ORD looks risky to me since you're arriving from an international destination and have to claim/re-check your baggage. ORD is quite an unpleasant place to be in the winter.

That layover in DEL looks positively brutal. Remember you're going to have to book DEL-SIN at 20:30 on the 25th, as you arrive into DEL 00:45 on the 25th. You won't be getting into SIN until the 26th. That means you have a 20h layover which will require you to get a transit visa. Getting a transit visa is a pain in the arse - as the Indian consulate won't issue it with more than 14 days validity from the date of issue and since you're leaving a week before, there's a real risk your passport can be tied up in processing.

I'd much rather go ZRH-PEK on the 24th, connecting through ICN or HND to get to SIN. It's hard to get a lot of these direct routes during Chinese New Year it seems!