Firstly, your solicitor will tell you the precise position on this. It's not straightforward and it is important. The date tax is due is determined by the 'date of probate'. You can exercise some influence on this date. It can be set as the date of death, but you may find it preferable to have it set as the date on which probate is granted.Inheritance tax will be due in the October following the date of probate. So, if you can submit your request for Probate at the very end of Sept. and hope for grant of probate in October, you'll have the whole year before you have to pay the tax. However, everyone else is also doing this , so the Probate office gets inundated at this time and this can lead to a delay in grant of probate. This may be ok for you, it may not ( if you need some money to pay bills). You need your solicitor to be pretty proactive with the Probate office for you.
In particular, be wary of finding yourself with a date of probate is the summer, creating a tax liability in that October, by which time, you may not have completed the liquidation and distibution of the assets. It happens.