1. Peter is usually on time, but he is late today.
2. Although Peter usually comes on time, he is late today.
Both of these sentences correctly combine the two statements and maintain their original meaning. The first sentence uses the coordinating conjunction "but" to contrast the usual punctuality of Peter with his current tardiness. The second sentence uses a subordinating conjunction "although" to show that Peter's lateness today is unexpected given his usual ability to arrive on time.