what is the usual time to start applying for jobs and other positions during a phd? I have started writing my thesis ( just yesterday:) ). My advisor asked me to submit it in one or two months. Now am wondering should I start applying for jobs at this time period. I plan to talk about this with my advisor. But I thought of other opinions as well. Please share your experience also.
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.