We consider the M/G/1 queue with an arrival rate lambda that depends w
eakly upon time, as lambda = lambda(epsilon t) where epsilon is a smal
l parameter. In the asymptotic limit epsilon --> 0, we construct appro
ximations to the probability p(n)(t) that n customers are present at t
ime t. We show that the asymptotics are different for several ranges o
f the (slow) time scale tau = epsilon t. We employ singular perturbati
on techniques and relate the various time scales by asymptotic matchin
g.