[For the seek of clarity, I summarize the answers and comments in this answer.]
The aim of my question was to understand better the structure
Number + MW + 多 (+ Noun), as I still had some doubts from the linked posts. After all the comments and answers, I think the meaning of the structure comes closer to the English expression and something:
Number + MW + 多 (+ Noun).
Number of MW and something; something between the Number of MW and a unit larger.
In the example:
We walked for two hours and something; something between two and three hours.
This works also for the case:
Number times some power of 10 + 多 + MW (+ Noun).
Number times some power of 10 and something MW; something between the Number times some power of 10 and that power of 10 larger.
We walked for twenty and something hours; something between twenty and thirty hours.
So, answering my questions:
Could you still express with the same structure an approximation that can be more than one MW larger? (And maybe less than some other larger MW value).
In the example, this approximation could be: We walked for more than two hours (but less than four hours). If that is not possible, how could you express this situation?
我们走了[至少]兩个小时。 = We walked for [at least] two hours
我们走了[超過]兩个小时。 = We walked for [over] two hours
我们走了[不止]兩个小时。= We walked for [more than] two hours
Maybe using 几? (They mentioned in some of the other posts' answers that 几 could used for larger approximations when you don't know its limits).
(Tang Ho): 几个小时 means more than 2 hours but not close to ten hours.
Thus, more or less the same as in English as 几 means several:
We walked for several hours.
(Dan, Tang Ho):
Number + MW + 多 (+ Noun) has a similar meaning to
Number + (Number + 1) + MW (+ Noun).
Like in English. The example：
We walked for two hours and something.
Can also be expressed as:
We walked for two, three hours.