TWR's suggestion to reference Porpoise Bay is probably the easiest solution.
If you have a printed copy of the Pt. Atkinson tables, here are the corrections for sites along Sechelt Inlet from my copy of the Sunshine Coast and Area Tide Tables booklet:
Egmont
High Tide: Add 10 min. add 1.1ft.
Low Tide: Add 9 minutes subtract 0.1ft.
Skookumchuck Narrows
Add 1hr. 45min. plus 5min. for each foot of rise, 7min. for each foot of fall
Porpoise Bay
High Tide: Add 2hr. 50min, subtract 6.9ft.
Low Tide: Add 2hr., subtract 1.9ft.
That said, Tuwanek is one of the least current sensitive sites around here that I can think of, even on big exchanges you have to really pay attention to notice the water is moving.