I took a clearblue pregnancy test and after a few minutes, a very thin, thread like vertical line and very very faint was there, then the next day it was darker but still very thread like, what does this mean, is it positive?

The next day it means nothing, except you did not throw it away like most people do.

It has to be read within the time frame given on the test.

If you saw a thin line shortly after the test, and that line indicates a positive result based on that test, then you're pregnant. A thin line is still a line.

As for the day after, it means nothing. Like Chuck said, all tests must be read within a certain time frame. A day later is way too long to read the results, so those results would not be valid.