As Exdc indicates, it takes a few months to get to the sentencing point if the defendant pleads guilty. If the defendant pleads not guilty, 9 to 15 months is probably a more realistic time frame.
A 'Section 18' charge is extremely serious. It's only one step below 'attempted murder' and carries the same maximum penalty of life imprisonment. The type of injury leading to such a charge is indicated in paragraph 55 here:
http://www.cps.gov.uk...on/#Unlawful_wounding
You'll see that paragraph 55 is in the (less serious) 'Section 20' part of that document. Scroll down to paragraph 65 to see the type of reasons why a 'Section 20' charge gets raised to 'Section 18'.
The sentences below refer to a first-time offender who is convicted after a trial. An early guilty plea can see the sentence cut by one third (but previous conviction can see sentencing increased). People sentenced to less than 4 years imprisonment normally spend half of their sentence in prison. Those with longer sentences can apply to be released at the halfway point but, if refused, they'll normally be released after serving two thirds of the term handed down by the judge:
For the least serious level of 'Section 18' ("Category 3"), judges are obliged (unless there are very exceptional circumstances) to pass a sentence of between 3 and 5 years imprisonment. For "Category 2", it's 5 to 9 years. For "Category 1", it's 9 to 16 years.
Chris