I've noticed that carbon offsets are usually sold by the tonne of CO2 equivalent, without any information about when that offsetting will occur
Of course they don't tell you when that offsetting will occur.
Carbon offsets are a major con. If you for example pay to reforest some land, if you do so by purchasing the land to be reforested and reforest it yourself (or pay someone to plant the forest), you as the landowner will get to decide how the forest will be used in the future.
If you on the other hand are foolish enough to pay for these ridiculous "carbon offsets", most likely they plant the forest somewhere and then the landowner who was paid to reforest the land can 10 years later chop it down, and if the landowner doesn't chop it own immediately, it would probably have been reforested anyway without the "carbon offsets".
Also you'll find that these "carbon offsets" are often multiply counted, so the same CO2 reduction is sold to three or more different buyers of "carbon offsets" who fail to realize they essentially bought the same offset.
The only ways to possibly cause environmental benefits are:
- Buy carbon permits but don't emit the carbon. (However, if enough many people will do this then the policymakers will take a note of this and increase the number of carbon permits available, so this is not a foolproof way.)
- Reduce your carbon dioxide emissions for example by becoming vegan, or buying an electric car, or starting bicycling, or switching to geothermal heat pumps, or living in a house built from wood as opposed to concrete. (However, if you do this in an area where carbon permits are used, one person reducing carbon emissions causes the carbon permit price to decrease, causing other people to emit more carbon dioxide, so this is not a foolproof way. However it's very good risk management to reduce your emissions intensity to a minimum.)
- Store the carbon in the form of biochar or forest stock or lumber or buildings made from wood in a land owned by you. (However, if enough many people start doing this then the policymakers will take a note of this and increase the number of carbon permits available, so this is not a foolproof way.)
- Vote! By voting someone who prefers large CO2 reductions very soon, it's more likely such reductions will happen very soon.
Note "carbon offsets" are not on this list.
Is there some kind of standard that defines when carbon offsets need to be realized?
Such a standard would be contrary to the interests of these conmen who sell these carbon offsets. Thus, no such standard is there, and no such standard will be there.