Short-time relaxation of the critical current in oriented grained ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{\mathrm{x}}$ and granular (Bi,Pb${)}_2$ ${\mathrm{Sr}}_2$${\mathrm{Ca}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{\mathrm{x}}$

The time-dependent behavior of the critical current density $j_c$ is investigated by ac inductive measurements. The variation of db/dt of the ac field between 0.1 and 3 T/s reveals a short-time relaxation in the millisecond regime before $j_c$ exhibits the familiar logarithmic decay. At fields above the irreversibility line only this short-time relaxation is observed. Our experimental time scale allows us to obtain the unrelaxed critical current density $j_{c0}$ at certain fields and temperatures.