Therefor We let loose on them a raging wind in evil days, that We might make them taste the torment of disgrace in the life of the world. And verily the doom of the Hereafter will be more shameful, and they will not be helped. [41:16]
And as for A'ad, they were destroyed by a fierce roaring wind, Which He imposed on them for seven long nights and eight long days so that thoumightest have seen men lying overthrown, as they were hollow trunks of palm-trees. [69:6-7]
Where is the contradiction? The only thing apparent is that the person who is making the argument is using deception, why? Well surah 54 verse 19 says NOTHING about the people of Ad being destroyed, from where did the missionary get this? All surah 54 verse 19 says is that Allah carried out a punishment of the people of Ad on a day of contestant calamity for them, it does not say that this constant calamity lasted for a day only! The next passages tell us how long this punishment lasted, with surah 41:16 telling us it lasted for a couple of days, and then in surah 69:6-7 it became specific saying that the punishment lasted for 7 nights and 8 days. And also notice that surah 54:19 and 41:16 do not say they were destroyed, all it says is they were punished, but lastly in surah 69:6-7 when Allah gives the specific number of days he also mentions the fact they were destroyed.
So what we can see is that surah 54:19 is a description of what happened, and so is 41:16, while 69:6-7 is the full detailed specific of listing the total amount of days and the eventual destruction of the people of Ad. And again I would like to ask the missionary WHERE DOES SURAH 54:19 say that the people of Ad were destroyed in a day, the text does not say that!
It is rather amusing though, because the only way the missionary can come up with an apparent contradiction is when the missionary makes things up in the verse! You see this proves that missionaries cant actually find any contradictions in the Quran, all they can do is make something up which is not indicated in the verses and the argue from there, this is what you would commonly call straw man.
Let me use an analogy as well, for instance a soldier talking about a war he will say:
?on 21 February war broke out, and it was a day of constant bombings and killings, it was dreadful, this war lasted for several days, it lasted for 8 days to be exact'.
Tell me does the soldier contradict himself? Not at all! This is exactly the same situation you have with the Quran, the missionaries don't quote in context, and they also go on to make things up. So therefore there is no contradiction, just a straw man attack, and a quoting out of context, how typical!
And Allah Knows Best!