what is the usual time to start applying for jobs and other positions during a phd?
Yes, you should start applying for jobs.  You should have started several months ago, since it can take time to find a job, and after you do it may still take some months before the job actually starts.  This depends strongly on what kind of job it is.

Of course, if you are looking for an academic job in the US, the interviewing season is roughly November-March, so you want to time things around that.  For industry jobs and academic jobs elsewhere, there is not usually a particular season to focus on.