Open source project – Contributor not responsive?

I have just started an open source project on GitHub for a Python library, and marked several issues as 'Good for starters' since I want to promote others trying to contribute and develop their skills, and get some help on the project in the meantime.

A new contributor commented on the saying he'll take it upon himself, so I assigned him to the issue, but since there (been 2 days now) he's been unresponsive (completely). How would I handle this situation and how long should I wait before I just decide to do it myself and unassign him?.. The issue branch had no code pushed from the moment it was made either.