I know I don't have a clear understanding of SSDI, but I do recall reading something along the lines that people shouldn't go from full time to part time employment for too long a period of time prior to filing as the SSA bases your SSDI payments on your last 10 quarters of earnings?

I know I'm not giving totally accurate information, but want to encourage you to research this aspect thoroughly prior to switching to part-time employment for an extended period of time so it doesn't permanently impact your SSDI benefits when you do apply.