Savings is very important in personal finance.
If you're working at an entry-level, you may want to consider spending your money on some basic needs first before you think about savings.
Some might want to consider working for some months before they start saving.
In any case, saving is very important, and if you have don't have any financial issue to deal with, nothing should stop you from saving immediately after your first salary.
However, if you are interested in saving from your first salary, the followings may prevent you from doing so until you get rid of them.
If you are owing friends and family members before you get your first job, it is important you clear the debt before fro the salary before you consider savings.
Having got a new job and you may need to change your wardrobe to step up your appearance and look more presentable.
Apart from this, you may also have to consider getting your own apartment and other basic needs before you start saving for other important goals.
These two are financial goals in their own right and once you settle your debt and meet those basic needs, you should be able to focus your attention more on saving for bigger goals.
However, it is difficult to say certain amount has to be in your account before you start saving. If you don't have financial issues, save. the sooner you start the better.