collocation - Using "some" to describe units of time

"some minutes, some years, some seconds" are grammatically incorrect.

But "a few minutes, a few years, a few seconds" works.

I'm trying to teach a non-native speaker this nuance but "it just sounds weird" does not feel like a satisfactory explanation. I know it has to do with count and mass nouns, because some time is correct and a few time is not, and time is a mass noun, and few can only be used with countable nouns. Minutes, years, seconds, etc. are all count nouns.

But, some can in some circumstances be used with count nouns and in others with mass nouns. What's the distinction I'm missing?

From your input I have gathered that some + time unit isn't technically wrong when used unselectively, (the "selective" sense of some is explained by Max Williams) but that it's just awkward in some cases. You don't need a some in any unselective construct with a unit of time. Years ago, for decades, in minutes, months later, over days.

Why does it sound awkward? Here's my highly heterodox and basically epistemological explanation. My first argument is that some isn't a totally amorphous quantity, that is, it actually does tell you some info about how much stuff (or how many things) it describes. I think we assume some to be countable, not in the sense of "a count noun", but in the sense that we can readily fathom its size. And furthermore I think that some connotes a smallish number, small enough so that it's readily fathomable, generally like 1-100. (This maximum "some-bound" increases for multiples of 5s, 10s, etc.) I'll give an example. Compare "I have not eaten meat for some years (now)" to "scientists believe that the earth was formed some years ago". The latter just sounds ironic. So, some sounds weird when used unselectively with large quantities because it seems to conflict with their size.
Some also sounds weird with with very small quantities because it appears to provide little information. This is because we assume that the unit of time was chosen efficiently. We don't expect someone to say "2400 minutes" because it's much easier to say "40 hours". We define very small units by their part of a whole, and we assume that at a certain point someone will start using the next order of magnitude unit. If the unit is chosen efficiently then some does not tell you much about quantity, because the coefficient will stay small, and we assume "some"-size by default unless told otherwise, and some-size is small. In these cases, some is vestigial and should be dropped.
But there's a happy medium where unselective "some" works with countable nouns. It's middle-of-the-range units of time where some begins to serve a purpose. It actually does give a bit of info about the actual quantity of the many things/much stuff. For example, "some years ago" is differently nuanced than just "years ago", it sounds somehow smaller. That justifies including the "some" even though it's correct without it.

Answer

I suspect that it is because "some" implies a selection, like saying "some of the minutes": ie, it implies that there is a list of possible minutes, each of which is a different object, and you're referring to some of them. This works if you are talking about people or cars: there are a finite amount of cars or people, all unique, and you can point to your selection and say "Here are some of the people.", or "Here are some people.".

However, units of time don't work like that: individual minutes aren't unique items you can select from all the possible options. They're more abstract. So to say "some of the minutes" feels wrong, and "some minutes" is a contraction of this so feels wrong too.