evam - in this way; vām - for both of you; tapyatoḥ - executing austerities; tīvram - very severe; tapaḥ - austerity; parama-duṣkaram - extremely difficult to execute; divya-varṣa - celestial years, or years counted according to the higher planetary system; sahasrāṇi - thousand; dvādaśa - twelve; īyuḥ - passed; mat-ātmanoḥ - simply engaged in consciousness of Me.

Thus you spent twelve thousand celestial years performing difficult activities of tapasya in consciousness of Me [Kṛṣṇa consciousness].