I just want to know why submission time is varying for submitting the same solution?

Example :

Solution A1 : Link — Submission Time — 31 ms

Solution A2 : Link — Submission Time — 15 ms

Both Solution-A1 and Solution-A2 are same. But still, both are taking different Submission time. Why?

Solution B1 : Link — Submission Time — 30 ms

Solution B2 : Link — Submission Time — 15 ms

Similarly, both Solution-B1 and Solution-B2 are same. But still, both are taking different Submission time.

May I know the reasons behind the different submission times?

Note: These both solutions are not mine, I am just wondering for the reason why these both same solutions are having a time difference.