I would propose the following policy:

1. All tools per default work only on the respective time step of the reference data and the segmentation, that are indicated by the currently selected time point (SliceNavigator). So this is general and independent from the fact if it is a 3D or a 4D segmentation. This is the same behavior like the interactive tools and does not break user expectations.
2. It is up to the specific tool (must be discussed there) if for 4D reference images others then the current time step of the reference data step should be used. Per se, I would say no.
3. It is up to the specific (3D) tool to allow the altering of more then the current segmentation time step (if the segmentation is 4D). If one wants such a feature I would add e.g. a check box to the tool like "confirm for all time steps".

In T27509#204970, @floca wrote:

I would propose the following policy:

1. All tools per default work only on the respective time step of the reference data and the segmentation, that are indicated by the currently selected time point (SliceNavigator). So this is general and independent from the fact if it is a 3D or a 4D segmentation. This is the same behavior like the interactive tools and does not break user expectations.
2. It is up to the specific tool (must be discussed there) if for 4D reference images others then the current time step of the reference data step should be used. Per se, I would say no.
3. It is up to the specific (3D) tool to allow the altering of more then the current segmentation time step (if the segmentation is 4D). If one wants such a feature I would add e.g. a check box to the tool like "confirm for all time steps".

As an additional remark, because it came up lately. In my opinion the time point, that was selected when a static mask was generated for a dynamic image, is irrelevant (a static mask always covers the whole extend of the dynamic image). For using the tools it should only be relevant which time step is currently selected.