The null hypothesis (H0) is that the mean (μ) is 4 minutes. The alternative hypothesis (H1 or Ha) in this case is that the mean>4 minutes. The purpose of hypothesis testing is to carry out a test which determines whether (within a specified confidence interval) the null hypothesis is to be rejected. When it is rejected it makes it more likely (but not certain) that the alternative hypothesis might be true.
The test usually establishes a critical p-value. If the test results are more extreme than this value (lower than), the null hypothesis has to be rejected within the frame of the specified confidence interval.