Yes, a 90-day waiting period is still slightly more expensive than the 180-day one but when you look at the difference, the "value" of the 90-day one is quite obvious since the premium difference might be as little as $30-50 per year.
I don't think that's "obvious" at all. You can easily go overboard with "oh, it's only a few dollars more" stuff.
I would usually recommend cover till 65 years old with a 90-day waiting period. The age is definitely more important than the waiting period.
Agreed with respect to the term to age 65. I'll make a few more comments on that point below....
As for age 55, it's definitely a risk I'm taking as I aim to part-time/semi retire around that age. Well if I don't make it...please pray for me.
The reason I lean in favor of a term to age 65 is that it's that much tougher to save for retirement when you're collecting DII benefits. So even if you plan to retire at age 55 (and even if that's a
realistic plan), the ability to afford to do so works better when your DII payout stream runs past age 55.
However, if you've managed to pile up a lot of CPF savings -- maybe a generous grandparent, aunt or uncle deposited the whole Full Retirement Sum in your CPF Special Account when you were born? And topped up your MediSave Account, too? -- then maybe converging on age 55 makes sense, when that big pile of CPF dollars becomes available and, if big enough, can bridge to age 65 and CPF LIFE.
Also keep in mind that DII payout streams are generally fixed nominal payouts, meaning their real value erodes over time due to inflation. Aviva sells a 3%/year escalating DII payout plan, but the 3%/year escalation is only applied once payouts start, not from the sum assured. So running the DII term out to age 65 (or at least age 60) could help conserve other savings/assets that'll have to do progressively more "inflation gap filling" in the out years, at least with the non-escalating payouts.
You can also combine/"layer" DII plans if you wish, for example $3,000/month escalating to age 65 from Aviva and $2,000/month non-escalating to age 60 from Great Eastern. As long as $5,000/month represents 75% or less of your gross employment income, that should be fine. (Aviva's MINDEF/MHA group DII policy is different in this respect, limited to 50% replacement. So that particular group rider doesn't combine as well.) [Why $3,000/month for Aviva? Well, they require a $3,000/month minimum to qualify for their premium reduction "promotion" (which never seems to go away).] The idea with this combination is that you'd get some more favorable policy terms from Great Eastern and (perhaps) reduce the term to align with children growing up and leaving the nest, requiring less household income to support a particular lifestyle. Anyway, the basic point is that you can fine tune the coverage in various ways.