Depending on the context, 正好 might work for you also.
[modif: 正 just + 好 good]
2 chance to, by coincidence
Wǒ zhènghǎo nà tiān xiàwǔ méi kè, kěyǐ péi tā jìnchéng.
It happened that I did not have class that afternoon, so I could go to town with her.
This is more of a "just as it happens" kind of phrase but that could also totally fit your, "right at that time," depending on the, specific, context, of course. If you mean in the sentence that mark, just happened to - by chance (maybe you called him many times and on the last try...) heard your voice then 正好 can work here also.