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Some part of magnet develops resistance so magnet will act as R-L circuit. A circuit that includes both a resistor and an inductor, and possibly a source of electromotive force, is called an R-L circuit. The inductor helps to prevent rapid changes in current. Apply Kirchhoff鈥檚 loop rule in R-L circuit then on solving differential equation of current, current in R-L circuit is calculated.

Current in R-L circuit is given by equation,

$i=\frac{蔚}{R}\left(1-e^{-\left(\frac{R}{L}\right)t}\right)$Where I is the current in circuit,$蔚$is emf, R is resistance, L is inductance and t is time.

Solve above for t to get,

$$\begin{gathered} t=\frac{-L}{R}\left(\ln \frac{i}{i_0}\right) \\ t鈭�\frac{1}{R} \end{gathered}$$

Hence, magnet develops resistance which means the resistance increases and time will be shorter.

Therefore, the correct option is (a)The time will be shorter because the resistance will increase.