In the off-chance someone comes across this post in the future I thought I should clarify the final outcome. FoxAsteria is correct. However, it should be pointed out that there are TWO "set time selection to items" in the actions list. The first is SWS and adds in parenthesis "(skip if time selection exists)". This is what I was doing wrong. The second "set time selection to items" at the bottom of a long list without the parenthesis works as expected.
Ok so I was a moron ... should have seen that sooner.
Thanks @Fox for the support.