Time is handled in a numerical way with Excel. Fortunately, you can generally produce the results you wish without having to delve too deep in mathematics. Time will mean both the clock time as well as the calendar time. Perhaps the easiest way to look at time is to examine some options.
If you examine your choices, you can probably find a suitable date format for any spreadsheet.
First
select the cell(s) you wish to format as dates (or times). The n choose
Format + Cells from the Menu.
Click on the Number tab and scroll down until you highlight Date.
When you do, the different choices for formatting dates will appear on the right panel.
You will select the proper format and click on OK to apply your choice.
You might notice there is a scroll bar for the different types. This indicates there are still more choices. The remainder of the choices are displayed here.
We don't find the like between the type selected and what Excel actually displays will always match our choice of cell entry. A short table is provided which shows what happens when you enter a single date different ways and a few of the different formats are applied to that data entry.
The yellow strip represents some of the choices of date formats. The left column represents several ways to enter April 5. The results are displayed in the table contents. Note what happens if you should enter the year first as is shown in the bottom two rows.
Comment: if you should enter 4/5 in a cell planning this entry to be a division problem, Excel will anticipate this is your way of entering a date and display the results using a date format of 5-Apr. The trick is to "fool" Excel into thinking the entry is a text. You should first enter an apostrophe and then 4/5 as in '4/5. Excel says this must be text and will display the 4/5 without the apostrophe showing. This apostrophe "trick" works for Time also.
Formatting
cells as time is very similar to formatting cells as dates.
First select the cell(s) you wish to format. Then select Format + Cells from the Menu.
Click on the Number Tab.to bring up your choices of categories.
When you slide your mouse down to Time and select, you will see the time format Types that are available to you. Note the scroll bar indicating even more choices.
As with the Date format above, an example might help you see which of the date formats would be most useful. Only a few of the total options are presented. The yellow strip represents three choices for formatting. The left column represents several ways to enter 9 O' Clock. The contents of the table show what happens.
Note that 9 and 0900 do not respond well as data for time. The use of the colon gave Excel sufficient information to use the time-formatted cells. Perhaps you can find a different time format which will "like" 0900 as a valid time entry...these three didn't!