> Do enyone have a view about when and in what order the occurence of
> the following types of ablaut/wovel changes occured?
> coloring of wovels by laryngeals
> quantitative ablaut (lengthened grade)
Sanskrit (and one or two other languages) shows signs of laryngeals in its
earliest stages. In particular for your purposes, ablauting -o- is treated
differently from -o- < -h3e- /-eh3-. The ablauting -o- appears long in an
open syllable, whereas the laryngeal-coloured -o- does not. This means that
the two main sources of -o- in IE languages were still distinct in Sanskrit.
Wovel colouring may therefore be quite late.
Quantative ablaut is hard to establish. It seems to have two main sources:
(a) lengthening in the nominative of animate nouns ending in -r, -n, etc
(b) lengthening due to laryngeals.
These two give entirely different patterns.
(a) e: ~ e ~ Ø and o: ~ o ~ Ø
(b) (*eH ~ oH ~ H) > e: ~ o: / a: / e: ~ a (Skt i) ~ Ø
The first is likely to be earlier, since it appears across all IE languages,
and no IE language shows the *-s we might have expected in that context.
The second type is much later, since laryngeals appear to have to survived
into the earliest stages of some of the daughter languages, and different
languages show slightly different reflexes.