What do you think is the difference between a two sample t-test and independent sample?

You can absolutely use the t-test with n-value > 30, it is below 30 when some people question its use. I don't follow you SD concerns. Do you mean the population SD and the sample SD?

Comment, you are probably fine using this data but is it really continuous? Can you have 2.5 hires? Or is it count data?