Improve estimated StartTime calculation in Aggregation

[karianna]

 * todo: The better way to do this is to calculate the variance in GC frequency and if the gap between 0.000 and
 * the first event exceeds the variance, then the first event would be considered the beginning of the log file.
 * otherwise, the time of the first event should be the time of the first event - the variance.

This removes the 0.25 magic number.

[kkdlau]

Hi @karianna, looks like the scope of this issue is well-defined and I think I will be able to handle this - would you assign this issue to me 😄 ?

[karianna]

Hi @karianna, looks like the scope of this issue is well-defined and I think I will be able to handle this - would you assign this issue to me 😄 ?

Please go ahead and thank you!