Don't think it'd be too bad, but if you're coming from Carindale, you could also catch a 222 to Buranda Busway where you can still hop on a 209, but also a 139 or 169 that all run to UQ.
139 doesn't operate on Saturdays. The 169 also syncs up badly with the 222 (169 departs 1 min after the 222 leaves), so beware that. You may be better off just changing to a 66 at Mater Hill.
On the whole, the 209 is pretty reliable and often runs a bit early, mainly because nobody is travelling on it on a weekend because there's no undergrad classes occurring (just a few postgrad ones).