What is the right formula to use in Excel?

I'm trying to average a set of ongoing number entries in excel. I have 14 and growing columns(days of input) of 24 rows(hours data is recorded) and a 25th row to average all the rows above it for a daily average(example: =AVERAGE(D3:D26)). Then I am trying to average the daily averages for an overall total average (Example: =AVERAGE(28:28)). My problem is that my unfinished columns that will be filled eventually cause a #div/0 code in their respective daily averages, and it reflects to the overall total average and also gives a #div/0 code. What formula can I use to get correct results? Thank You.