What is the correct definition for 0 seconds?

The Absence of all Magnitude or Quantity

Arithmetic sequence   is a  sequence   of numbers such that the difference between the consecutive terms is constant. 

a  geometric sequence , is a  sequence   of numbers where each term after the first is found by multiplying the previous one by a fixed, non-zero number called the common ratio.

0.2 - 0.4 = -0.2
0.4 - 0.6 = -0.2
0.8 - 1.6 = -0.8
therefore, not an arithmetic sequence

0.2/0.4 = 0.5
0.4/0.8 = 0.5
0.8/1.6 = 0.5
therefore, it is a geometric sequence

hope this answers the question. have a nice day.