SB 7.5.54

yadācāryaḥ parāvṛtto
vayasyair bālakais tatra
 sopahūtaḥ kṛta-kṣaṇaiḥ
yadā — when; ācāryaḥ — the teachers; parāvṛttaḥ — became engaged; gṛha-medhīya — of household life; karmasu — in duties; vayasyaiḥ — by his friends of the same age; bālakaiḥ — boys; tatra — there; saḥ — he (Prahlāda Mahārāja); apahūtaḥ — called; kṛta-kṣaṇaiḥ — obtaining an opportune moment.
When the teachers went home to attend to their household affairs, the students of the same age as Prahlāda Mahārāja would call him to take the opportunity of leisure hours for play.

In tiffin hours, the hours when the teachers were absent from the classroom, the students called Prahlāda Mahārāja, wanting to play with him. As will be seen from the following verses, however, Prahlāda Mahārāja was not very much interested in playing. Instead, he wanted to utilize every moment for advancing in Kṛṣṇa consciousness. Therefore, as indicated in this verse by the word kṛta-kṣaṇaiḥ, at the opportune moment when it was possible to preach about Kṛṣṇa consciousness, Prahlāda Mahārāja used the time as follows.