the different length of your results, and especially the trailing "M" in the last line made me suspect gettimeofday doesn't return integers. A look into Time::HiRes confirms

gettimeofday ()
In array context returns a two-element array with the seconds and microseconds since the epoch. In scalar context returns floating seconds like Time::HiRes::time()

print evaluates its arguments in array context. So you could either change $, ($OUTPUT_FIELD_SEPARATOR) to somethng visible, or force scalar context by printing scalar gettimeofday or gettimeofday+0.