Abstract: In the age of mobile internet, there is growing social pressure for instant responses in online communication. While response timeliness (instant vs. delayed) may yield divergent interpersonal effects, existing research lacks systematic investigation into these dynamics, particularly regarding underlying mechanisms. Grounded in Expectancy Violations Theory (EVT), this experimental study examined how response timeliness and power relations jointly influence interpersonal impressions. Results revealed: (1) for the recipients, instant reply leads to positive interpersonal impressions, while delayed reply results in negative ones; (2)expectancy violations mediate the relationship between response timeliness and interpersonal impressions; (3)compared to those with low power, individuals with high power who received delayed reply experienced higher levels of negative violations, leading to more negative evaluations of interpersonal impressions. These findings illuminate the psychological mechanisms through which response timeliness shapes social perceptions, offering practical insights for managing digital communication strategies across power asymmetries.

Key words: social networking software, instant reply, delayed reply, expectation violations, interpersonal impressions