It's interesting to observe a word changing its spelling. I think sooner or later we'll be spelling than as then.
On Sunday morning I was listening on my car radio to The Big Backyard, a gardening program. I might have misheard, but it seemed the presenter (I think her name was Millie) said 'then' in a sentence where I would have expected 'than'.
This is the first time I've noticed this usage in speech, and maybe I misheard.
However, it's quite a frequent written transposition. For instance, when I was at the Royal Melbourne Show recently, I say this sign:
Daily Writing Tips, like many other internet sites, explains the difference between the two words. Basically, 'then' is used for time-related concepts and 'than' for comparisons.
But... this video clip from the Merriam Webster Dictionary puts the cat amongst the pigeons! Apparently they were previously spelled the same and it's a relatively modern practice to treat them differently. And 'than' can be used in some time-related concepts.
The Online Etymology Dictionary dates the differentiation from about 1770.
So I say, don't worry about it if you're confused. Just tell the critics you're a traditionalist and prefer the older spelling.