According to
GlobalSecurity.org, typical 105 and 155mm smoke shells burn for 40 to 90 seconds and screen for less than 15 minutes. That's for different shells apparently, and I'm not sure that info is up to date with the latest rounds. It's consistent nevertheless with the data I found on AFV-delivered smoke grenades, which burn for around 10-15 seconds and last around 5 minutes, depending on the wind. These grenades are much smaller and have a lighter payload than arty shells, of course.
Also consider that different technologies will have different effects. These shells quoted above as burning for around 1 minute are chemical-based smoke-emitting canisters. I don't know much about the chemistry involved, but obviously a WP burster will burn for much less time.
Hope this helps.
Re: Arty Smoke Info Request
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