Using an IF-Statement inside a drawtext (FFMPEG)

I'm currently trying to implement a timer on a video with FFMPEG, so it should start at 00.00 and start timing after a number of frames and stop timing again after a set amount of frames. So the timer should work like this:

00:00 00:00 00.00 (start timing) 00.01 00.02 [...] 05.88 05.89 (stop timing) 05.89 05.89 05.89

So far I've got the following as (minimal) command:

ffmpeg -i input.mp4 
-filter_complex "[0:v]drawtext=fontfile='C\\:font.ttf':
text='%{eif\\:n/30\\:d\\:2}\\:%{eif\\:((mod(n,30))/30)*100\\:d\\:2}':
fontcolor=black:fontsize=55:x=(1705.5-(text_w/2)):y=(1000.5-(text_h/2)),format=yuv420p" 
-pix_fmt yuv420p -c:a copy out.mp4

There is some more stuff inside of the filter_complex, so I can't replace that with -vf or similar.

Thanks for all of your help!