Given "after", "before", "when", "while", "since", "until" and longer
terms such as "from now on", "from this point forward" etc., how can we
collapse them? 

Before time T, an event happened
Until time T, an event was undergoing

Since the difference here seems to be between punctual/durative, which
can be marked on the verb, I collapse before and until. Same for since
and after and "from time x into the future"-rewritings.

"While" can be used to mark that something happened at the same time or
during something else happened: while X was happening, Y was also
happening. Not collapsible with before/until or after/since.

When "when" is synonymous with "once" as in "once we're there", "as soon
as we're there", it does the work of "after" with the added meaning of
immediacy, which can be separated out. "When" can also mean "at, during
or around some time T" as in "when the gods wandered the earth, ...",
"when I was younger than you are now, ...", "when I'm sixty-four, ...",
without the meaning of immediacy. This then points to a word left out
from the overview, "during", which was also mentioned for "while".

We have:
before, up to time T (before, until)
after, from time T (after, since)
overlapping in time, at time T (while, during, when)

In addition there are lotsa of words for time that does not attempt too
join clauses in any way, like "late", "last", "previous", "now", "then"
etc., these could also be interesting to collapse, especially in that
words like "last" has at least two meanings: "previous" and "final".