Hello there Lara -

My grammar book [by Butt & Benjamin] implies that there would sometimes be a very slight difference between "no más que ..." and "no más de ..." in the lesson which you are asking about, if we tried to replace the first option by the second one.

That^ book compares "J no compró más que 20 libros" = "J bought only 20 books"

with

"J no compró más de 20 libros" = "J bought not more than 20 books"; [i.e., he may have bought less; we are not sure].

So, I tried to apply that^ pattern-change in order to recast the sentences to which you specifically drew attention - but the revised versions sounded really awkward, such that they would be extremely unlikely to be heard in normal conversation -

e.g. "No llevo esperando más de unos minutos" would presumably be equivalent to "I've been waiting not more than a few minutes" - (which is of course essentially the same as saying "I've been waiting only a few minutes").

- . - . - . -

In a completely different context, the same grammar book gives a really 'colourful' illustration demonstrating how "más de ..." and "más que ..." can carry totally distinct meanings, and in addition it shows how Spanish avoids an ambiguity which cannot be distinguished in English without adding extra clarification:

[You probably know this already - because it is mentioned in a Kwiziq Lesson entitled "Más que/Menos que vs Más de/Menos de (More/Less than) (kwiziq.com) " - but this amusing example might help other students remember it]:

1. "J comió más que tres personas" 

and

2. "J comió más de tres personas"

both translate as "J ate more than three people".

But there is in fact no resemblance between the two:

1. "J comió más que tres personas" = "J ate more than three people would eat" -

and

2. "J comió más de tres personas" > J is a cannibal, and had a large meal consisting of more than three people !