Wiktionary
count in
vb. 1 (context transitive English) to include (someone) 2 (context transitive English) to do a countdown before the start of something, especially a musical performance.
Usage examples of "count in".
At which mouse should the cat have started the count in order that the white mouse should be the last eaten?
In the common ground and meadow in front of the church, an assembly had gathered by the chair and table where the count's chatelaine held court to choose young folk to serve for a year at Lavas Holding and to receive the tithes and taxes the village paid to the count in exchange for his protection in times of war.
I kept a running count in my head, and when I'd thought of exactly one hundred things that were less appealing than doing my duty, I stood up.