You’ll likely need to apply for probate within six months of the death of the person whose estate you’re dealing with.
Why? There’s no time limit when you can apply for probate after someone has died. But there is a six month time limit on starting to pay HMRC any inheritance tax (IHT).
Since you need to report the value of the estate to HMRC before applying for probate, and a grant of probate is sometimes needed to access bank accounts and pay IHT, most people tend to deal with these two processes together.