about this time; around now
Refers to the current approximate time or season. Can be used as a noun or adverb.
It's always crowded around this time.
今時分、桜が満開です。
The cherry blossoms are in full bloom about now.
Compound of 今 (ima, 'now') and 時分 (jibun, 'time, season'). The exact historical derivation is straightforward.