“What is the time, kot or? He pressed his repeater and, undismayed, it hissed and tinkled out ten twenty-one." (Note to Line 149)
The hissing repeater (watch) image is taken from Eugene Onegin, One: XVII, variant to lines 1-3 in the draft:
Onegin drinks, is noisy, but again
<under the finger hissing> his Bréguet
<informs him> that [a play] by Shahovskoy...
(Note: this Bréguet is a watch Nabokov describes as "an elegant repeater.")