It depends on how many tags there are and how you want to use them, of course, but if you can use tag history instead, you can set the timestamp source to “data”, which will use the OPC timestamp. Of course, you’ll have to decode it from the unix time format that it’s stored it, but that is easy enough.
Another option would be to use a transaction group with the tag, and then a copy of the tag which references the “timestamp” property. That tag would be a “date” type, and will store the OPC timestamp for the value.
Unfortunately the “valuechange” column can’t be the opc time, because in the external tag provider system it’s used to detect changes, but we could probably add another column, which is “data time”. I believe this has actually been requested a few times…