adverb, noun which may take the genitive case particle 'no'
on schedule; on time
Used when something happens exactly at the scheduled time. Often used with verbs like 出発する, 到着する, or 始まる.
電車は定刻通りに到着した。
The train arrived on schedule.
会議は定刻通り始まった。
The meeting started on time.
時間通り is more general 'on time' for any set time, while 定刻通り specifically refers to a scheduled or appointed time.
Compound of 定刻 (scheduled time) + 通り (as, in accordance with).