Interview Phone Call

Two days ago (Wednesday), I received a callback from an employer saying that they are interesting in setting up an interview with me and that I should call them back. I was not available right when they called me so I returned their call about 45 minutes later and was left leaving a voicemail for the employer. The issue I'm having now is that they did not call me back yesterday (Thursday) and I am concerned that poor cell service in the building impacted my voicemail. Is it inappropriate, even assuming that the voicemail is fine, to call again today (Friday)?

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