Lebesgue measure of the set $\{t\in[0,T],W_t\geqslant a\}$

Question

Let $(W_t)_{t\geqslant 0}$ be a standard Brownian motion, I am interested in the set $A:=\{ t\in[0,T],W_t\geqslant a\}$ where $T>0$ and $a>0$. In particular I want to evaluate the Lebesgue measure of this set, actually I don't know if the law of $\mu(A)$ or $\mathbb{E}[\mu(A)]$ are well known. I think the first Lévy's arcsine law (saying that $\mu(A)$ follows an arcsine distribution when $a=0$) might be useful but I have no clue how I could use it.