How to calculate time interval between current and voltage waveforms
For sinusoidal AC circuit, a useful term to remember is: -

C I V I L


For a (C)apacitor I leads V.
V leads I for an inductor (L)


In both cases, the leading/lagging is 90 degrees.

If the inductor or capacitor has resistive losses then the phase angle magnitude will be less than 90 degrees.