I'm assuming that you have tide tables but just in case you don't HW Oban today is 11:42 BST
The CCC Kintyre to Ardnamurchan cruising directions work for me, the info is in there but Claymore of this parish has generated a usefull little table:http://www.yotblog.com/claymore/2012/01 ... ate-chart/
which states that the west going stream starts +3:30 which would be about 15:10 today. It depends on you and your boat but I would motor out of Loch Craignish and give myself an hour and a bit to get there.
Having looked at the forecast a Westerly wind should push you along nicely but I would aim to get to Dorus Mor a bit before the tide turns in your favour because once the flow is well established I would expect a bit of a chop with the wind over tide.
Some of the folk who keep boats @ Ardfern will know better.