Why can I not have the date and time in one cell
Welcome to Ask Different. To get both date and time in a column, click on the column you wany this in, as in A or B or... After that make sure the Format button in top right of the sheet is selected. Then go to the sidebar on the right and select CELL. Near the top of the sidebar is a pull-down under the label Data Format.  Select Date and Time from the pulldown menu. Once you've selected this a date and time appear in a single cell. See figure below from numbers. I entered the date as 2/5/20 1pm and i got the number displayed in the image.



To change the value in the next cell add 1. This changes the day by 1, + 365 changes the year by 1. Fractions change the time. The value 0.000012 will change the time by 1 sec. And 60 times that, or 0.000694, changes the time by 1 minute.