The 10% rule refers to putting aside 10% of your income towards savings whether this is for your pension or emergency reserve fund.
This rule refers to the net income, the amount left after taxes have been deducted on your payslip. On a net income of 2,500 the 10% amount will be 250 (2,500 * 0.1 = 250).
Are you able to put aside 10% salary each month? I recommend reading my article on How to Create a Personal Budget Plan which walks through steps on how you can get the overview needed to figure out how your financial situation is.
Creating an emergency reserve fund
If you are operating with the goal to have 3 months of income saved in your emergency reserve fund, assuming no funds are allocated in the fund yet, it would take 30 months (2,500 * 3 / 250 = 30) to fully finance your emergency reserve fund.