Answer

“Addha-kāla” in Jain usage usually means a long period of time. In Jain cosmology, a kalpa or cycle of time is divided into two half-cycles: the ascending phase and the descending phase. ( jainpedia.org)

Explanation

If you saw it in a manuscript or devotional text, “addhā-kāla” can simply mean “for a long time” or “for an extended period.” In the broader Jain time-cycle teaching, a full cycle has two halves, each with six periods. ( jainpedia.org)

Takeaway

So, in simple words: addha-kal = long time / half-cycle of time, depending on context. ( jainpedia.org)