That time frame shouldn't cause any problems. Tide doesn't often become a major issue in Semiahmoo/Boundary Bay. Current can sometimes pick up through the entrance to Drayton Harbor, but rarely too bad. It'll be less than a knot during that time.
As you start to venture out, I'd recommend a good reference for tidal currents since this is difficult to predict using tide tables alone without a good amount of local knowledge. Even then it can be a bit of a black art. For example, the current tends to flow in a big counter-clockwise circle around the south end of Georgia Strait (Point Roberts -> Saturna -> Sucia -> Birch Point -> Point Roberts). This flattens out and flows south or north sometimes, and occasionally reverses to a clockwise direction. This is information that you can't get from a tide table, but which is very important when choosing a route.
There is a decent web site that can be helpful:
http://www.deepzoom.com/#/Views/Boat.xaml. This shows the direction and speed of projected currents at specific locations. This helps plan the best time to go past certain points, but can be very misleading because it only makes predictions at specific points. One might be lead to believe that if the current is flowing north at a point on one side of a strait, that the current would be flowing north throughout the strait, for example. This is rarely the case except in narrow channels.
A great reference, and one I don't leave the bay without is a publication put out by the Canadian government called "Current Atlas: Juan de Fuca Strait to Strait of Georgia". Here it is at Fisheries Supply in Seattle, but you can find it all over the place:
http://www.fisheriessupply.com/productgroupdetail.aspx?cid=130709&keywords=current+atlas. I think West Marine in Blaine sells it. It contains a bunch of charts showing the direction and speed of currents all over, not just at specific points. Each year you buy a supplement booklet that correlates a chart number with a date/time. Very easy to use and invaluable.
Check out the attached picture of one of the charts. You'll see what I mean. There is a big counter-clockwise current south, but a clockwise current up in the bay. Look at the currents NE of Orcas and SW of San Juan. This is why tide tables don't cut it in our neighborhood.
