I don't think you need to add the word "temporary". For mine, my employer wrote "this is to confirm the employment of xxx at xxx. She was employed full-time in the position of xxx. She worked 37.5 hours per week, wage was xxx". And my letter was accepted and approved.Yes, it is the same as temporary appointment! Is that something people mention? I changed things a bit and wrote:
"This is to certify that XYZ was part of my research team as a full-time Research Technician from 5th May, 2017 up to 6th October, 2017." Is that sufficient?
Or should I say, "
"This is to certify that XYZ was part of my research team as a temporary, full-time Research Technician from 5th May, 2017 up to 6th October, 2017."