You're probably right, but here's a very simple test I left running on my computer while heading to the gym:
Tester macro
Pause Until — How Frequently does it evaluate (with reduce CPU usage enabled).kmmacros (22 KB)
And heres the resulting data from my test:
Test completed in 88:35 minutes
Pause_______"Error"_______CPU
1 ms_______2 ms_______72.9%
1 ms_______2 ms_______109.2%
1 ms_______2 ms_______107.9%
1 ms_______2 ms_______108.9%
1 ms_______2 ms_______91.5%
2 ms_______21 ms_______98.3%
2 ms_______22 ms_______79.8%
2 ms_______22 ms_______81%
2 ms_______1 ms_______81%
2 ms_______22 ms_______128.1%
4 ms_______19 ms_______102.5%
4 ms_______20 ms_______100.8%
4 ms_______20 ms_______85%
4 ms_______20 ms_______73.4%
4 ms_______20 ms_______67.6%
8 ms_______15 ms_______66.7%
8 ms_______16 ms_______61.2%
8 ms_______16 ms_______61%
8 ms_______16 ms_______60.5%
8 ms_______1 ms_______51.4%
16 ms_______7 ms_______47%
16 ms_______8 ms_______41.3%
16 ms_______8 ms_______45.6%
16 ms_______8 ms_______46.1%
16 ms_______8 ms_______60.9%
32 ms_______12 ms_______56.6%
32 ms_______13 ms_______60.7%
32 ms_______13 ms_______54.3%
32 ms_______13 ms_______48.4%
32 ms_______13 ms_______43.5%
64 ms_______1 ms_______38.5%
64 ms_______2 ms_______34.8%
64 ms_______2 ms_______37.8%
64 ms_______2 ms_______44.9%
64 ms_______2 ms_______47.8%
128 ms_______21 ms_______45.3%
128 ms_______2 ms_______36.8%
128 ms_______22 ms_______30.2%
128 ms_______1 ms_______40.6%
128 ms_______15 ms_______96.5%
256 ms_______19 ms_______54.9%
256 ms_______20 ms_______73.1%
256 ms_______20 ms_______59.3%
256 ms_______20 ms_______138.5%
256 ms_______20 ms_______150.1%
512 ms_______15 ms_______78.6%
512 ms_______16 ms_______47.2%
512 ms_______16 ms_______31.1%
512 ms_______16 ms_______69.8%
512 ms_______16 ms_______46%
1024 ms_______7 ms_______64.1%
1024 ms_______8 ms_______74.8%
1024 ms_______8 ms_______67.2%
1024 ms_______7 ms_______158.1%
1024 ms_______16 ms_______119.8%
2048 ms_______12 ms_______45.6%
2048 ms_______18 ms_______153.8%
2048 ms_______6 ms_______30.5%
2048 ms_______16 ms_______32.4%
2048 ms_______11 ms_______53.4%
4096 ms_______6 ms_______39.4%
4096 ms_______5 ms_______45.3%
4096 ms_______11 ms_______37.5%
4096 ms_______2 ms_______31.3%
4096 ms_______8 ms_______31.8%
8192 ms_______21 ms_______108.6%
8192 ms_______12 ms_______37.3%
8192 ms_______2 ms_______33.1%
8192 ms_______11 ms_______119.9%
8192 ms_______9 ms_______33%
16384 ms_______134 ms_______32.3%
16384 ms_______140 ms_______34.1%
16384 ms_______146 ms_______106.8%
16384 ms_______155 ms_______69.2%
16384 ms_______149 ms_______57%
32768 ms_______297 ms_______28.5%
32768 ms_______290 ms_______35.6%
32768 ms_______294 ms_______32.6%
32768 ms_______280 ms_______35.3%
32768 ms_______288 ms_______27.1%
65536 ms_______4574 ms_______29.2%
65536 ms_______4586 ms_______40.9%
65536 ms_______4589 ms_______37.1%
65536 ms_______4595 ms_______39.1%
65536 ms_______4586 ms_______34.2%
131072 ms_______4062 ms_______73.4%
131072 ms_______4064 ms_______34.6%
131072 ms_______4063 ms_______42.1%
131072 ms_______4064 ms_______31.3%
131072 ms_______4060 ms_______33.4%
262144 ms_______304 ms_______38.7%
262144 ms_______3016 ms_______42.1%
262144 ms_______3018 ms_______33.1%
262144 ms_______3016 ms_______100%
262144 ms_______3023 ms_______126.6%
524288 ms_______929 ms_______30%
524288 ms_______932 ms_______120.1%
524288 ms_______951 ms_______39%
524288 ms_______939 ms_______36.5%
524288 ms_______922 ms_______45.5%
Nothing conclusive (of course, the way this test is set up), but the data seems to indicate that the Pause Until (with reduce CPU usage enabled) slows down evaluation frequency after about 10 seconds of reevaluating the conditions, and then again even more so after about a minute.