If you used
*/2 in some field, looking at
man 5 crontab:
The time and date fields are:
field allowed values
day of month 1-31
month 1-12 (or names, see below)
day of week 0-7 (0 or 7 is Sun, or use names)
A field may be an asterisk (*), which always stands for ``first-last''.
Step values can be used in conjunction with ranges. Following a range with ``/<number>''
specifies skips of the number's value through the range. For example, ``0-23/2'' can be
used in the hours field to specify command execution every other hour (the alternative in
the V7 standard is ``0,2,4,6,8,10,12,14,16,18,20,22'').
*/2 for day of month is 1, 3, ... and for day of week is 0, 2, ....
If you used the day of week field (going by the mention of Monday), then it would first run on Tuesday (since 0 is Sunday, 2 is Tuesday). If you used the day of month field, it would run on Monday if the date on Monday was an odd number, and on Tuesday otherwise.