So, if you are sure that it is first order as regards to Salicylic Acid, it is possible.
SA - Salicylic Acid
P - product of hydrolysis
If stoichiometric is simple as below:
SA -> P
C_SA(final) = C_SA(t=0) - C_P(final)
the rate law:
-d(C_SA)/d(t)=+d(C_P)/d(t)=k*C_SA
Now, you have to integrate it and put your data to obtained expression, only k is unknown.
BTW: it isn't good practice, you should try to get a kinetic curve (function of concentration in time) and try to fit the best value k to get the minimal sum of squared error (for example).