java – Will this time duration measurement in two threads give correct result?

A program I’m developing has two threads running similar but different task:

thread1:

timer1.start()
writeToExternalDB1(consumedData)
timer1.end()

thread2:

timer2.start()
writeToExternalDB2(consumedData)
timer2.end()

I want to compare the writing performance of the two external database. I have timers around the write operation so that I can collect some metrics. Those two threads are running concurrently.

My question is will this design give correct measurement result regarding to the time spent by each write operation?
My understanding is probably not because the processing time given by CPU to each thread may be different. Let’s say for thread1, after timer1 started, cpu will not move forward to the followed write operation, but switch to processing thread2 instead. This may introduce some gaps between timer1.start() and writeToExternalDB1(consumedData). However, in that case, should we regard this gap as negligible if we are processing a lot of data? What should I do to give the correct measurement result?