Time Shrinking denotes the psycho-acoustic shrinking effect of a short interval on one or several subsequent longer intervals. Its effectiveness in the domain of speech perception has so far not been examined. Two perception experiments clearly suggest the influence of relative duration patterns triggering time shrinking on the perception of tempo and rhythmical isochrony or rather “evenness”. A comparison between the experimental data and duration patterns across various languages suggests a strong influence of time shrinking on the impression of isochrony in speech and perceptual speech rate. Our results thus emphasize the necessity of taking into account relative timing within rhythmical domains such as feet, phrases or narrow rhythm units as a complementary perspective to popular global rhythm variability metrics.