if you were invoolved in an acid rain monitoring project with several other samplers,why would it be important that all of your samples on the same day and do the alkalinity tests within 24hrs

Samples from different days may not contain the same amount of acidity because amount of rain is different, amount of acidity is different, atmospheric conditions are different, and a host of other differences. The reason you want to determine alkalinity within 24 hours (and I strongly believe 24 hours is FAR TOO LONG to wait) is that CO2 and SO2 (two of the components of acid rain and some other components (NOx for example) behave the same way) is that these gases may not stay in solution so the alkalinity tests would be no good. Frankly, I think one should determine alkalinity within two hours of sampling time.