That depends on many things, including:
If the person you feel is at fault accepts responsibility or if we have to prove they were partly or fully responsible
What injuries you suffered and how likely they are to have a long term impact on you.
Accessing medical records, expert reports and working with insurance companies. Generally working with multiple parties can take a bit longer so can add to the time.
When you choose your personal injury lawyer you should go with someone you feel you can trust and will be comfortable working with for a bit of time as things can take longer than expected to settle.