Richard is correct. The TC1 track always reflects the project format. You are in a NTSC project which is defined as 29.97 (DF or NDF). 23.976 and 24 are manufactured frames from the NTSC video and are calculated as such with the readers, but not the TC1 ruler in the timeline.
The 1080 workaround suggested by Richard is the only solution as 24fps is a defined frame rate and SMPTE standard.
Would it be a nice feature to change timecode format in the rulers in the timeline? Yes it would.
Michael