Hi,

Yes, Subscription.setTimestampsToReturn(TimestampsToReturn.Both), with default value being TimestampsToReturn.Source.

It is not item-specific parameter: https://reference.opcfoundation.org/Core/Part4/5.12.2/#5.12.2.2, or well, there is multiple ways to think it, but at least it must be the same for a single bulk-createmonitoreditems, thus probably why it was made like this (changing it before adding items would cause items to use that one; though on a reconnect if the subscription was redone every item would use the setting of that time, thus in practice this value should be only set once before adding any items to the subscription).