Question about the correct variance to use

I am currently analysing a longitudinal study regarding a treatment group and measurements were taken over 5 intervals. (for example week 1, week 2, week 3, week 4 week 5 etc). There are in fact 10 subjects (for example 10 rats) in this group and I am interested to find out:

$\displaystyle H_0:\bar Y_{week2}-\bar Y_{week1}=0$, where $\displaystyle \bar Y_i$ is the mean weight of the rat at week i

I have done a proc mixed in SAS with unstructured covariance matrix as defined below:

Row Col1 Col2 Col3 Col4 Col5

1 21.5756 33.0196 31.5821 27.9476 23.2321

2 33.0196 68.7274 69.0607 60.7339 52.9107

3 31.5821 69.0607 94.7690 109.63 116.16

4 27.9476 60.7339 109.63 166.91 190.55

5 23.2321 52.9107 116.16 190.55 249.72

with $\displaystyle \bar Y_{week1}=54, \bar Y_{week2}=78.5 $ What should I do to test the hypothesis?

This is what I have done:

$\displaystyle \frac{78.5-54}{\sqrt{21.5756+68.7274-2(33.0196)}}=\frac{24.5}{\sqrt{24.2638}}=4.974$

Am I right to define the denominator as above? Is this a Z-test or t-test?

*Note that I have simplied my question to direct it to my doubt*