Every time I try to change it to 3.9 seconds, it jumps up to 4 seconds.
If someone could please come back asap that would be much appreciated.
What version of Premiere Elements and on what computer operating system?
How are you adjusting the duration of the clip to 3.9 seconds?
What is your insert - a jpeg still or something else?
I need more details, but, if you use Time Stretch to get your 3.9 seconds duration, it would look like 00;00;03;27 (hours;minutes;seconds;frames). The frame 27 is the counterpart of 0.9 seconds in a NTSC setup which uses 30 frames per second.
Please review, consider, and give more details.