Can you still use "Number + MW + 多" when the Number can be more than one MW larger?
How could you express the case when your approximation can be more than one MW larger? In the example, it could be: We walked for more than two hours.

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
All three above can refer to the amount of time beyond one MW larger.

Can you still use “Number + MW + 多” when the Number can be more than one MW larger?

多 in &quot;我们走了[超過/不止]兩个[多]小时 would be redundant, because &quot;超(over) and &quot;不止&quot; (more than) already indicated it is more than two hours
&quot;至少&quot; in &quot;我们走了至少兩个小时&quot; also implied 'could be more'
Edit:
Dan wrote:

More than two hours but less than four hours could be roughly 两三个小时

It works only when it is between two and three hours. Doesn't work beyond three hours
我们走了兩三个小时 means &quot;We walked two, three hours
(it also implies, not more than two hours by just a little; it has to be something between two and a half hours and three hours)