Excel x axis with asci labels at non-equidistant points

Lets say I have data like this:

Time    step   measurement
0:00:00 start   12.7
0:01:00 step1   25.3
0:10:12 step2   37.3
0:12:10 center  45.2
0:17:30 prelast 42.3
0:23:10 last    33.4
0:23:15 last2   27.2

Now I want this plotted with a time x-axis. I want x-tick markers where there is a time entry. I want the time and text from col 2 printed at the tick markers. The col 3 is the y-value.

Solution using gnuplot is also appreciated.

Thanks, Gert