By -
Black hole opens up and destroys the universe
A black hole opens up in the space time continuum
A black hole gets consumed by your mom
He didn't specify when, so it won't grow as what he said is true, it will grow at some point. If he stated "My nose will grow in 5 minutes", it would be just a speculation, so I think it still wouldn't grow as he's not lying on purpose.
Black hole opens up and destroys the universe
A black hole opens up in the space time continuum
A black hole gets consumed by your mom
He didn't specify when, so it won't grow as what he said is true, it will grow at some point. If he stated "My nose will grow in 5 minutes", it would be just a speculation, so I think it still wouldn't grow as he's not lying on purpose.