How long do you have to wait on a clearance certificate?

my grandfather died in september, and i am the executor of the estate inheriting everything, i have been waiting on the money since september and it is now april i tlaked to my lawyer today, she said as soon as the income taxes are paid she has to apply for a clearance certificate which says the estate doesnt owe anymore taxes, she said to me this could take another 12-18 months, can someone else tell me how long on average you have to wait on a clearance certificate?