I don't understand why you think it's too late to plant the Oxallis oregana out. If its outside now (adjusted to outdoor conditions), it should do fine if planted out. These plants are generally listed as hardy to zone 6 or 7, and your profile says you are in zone 8. They would likely fare much better planted out than if kept in a pot inside.

The O. triangularis might be a little different story since (depending on the variety) it may not be hard, or may be only marginally hardy, in your area. In warmer climates, like yours, hardy plants can usually be successfully transplanted any time from mid fall to early spring. Marginally hardy plants are probably best transplanted in spring.