Quick time entry: (Franz Pölt)

You would prefer to type 745 instead of 7:45. No problem! Enter the data as number first and apply the following formula later, by copying its values over the quick entered data.

=--TEXT(A1;"0\:00")   format cell as [hh]:mm

To be more precise in time use one of the next two formulas:

=--TEXT(A1;"0\:00\:00")   format cell as [hh]:mm:ss, enter 74500 in A1 
=--TEXT(A1;"0\:00\:00\.000")   format cell as [hh]:mm:ss.000, enter 74500000 in A1

761 converts to 8:01, 76161 returns #VALUE!, and a typical sledding time (3rd formula) is 104979.

Don't forget: You do not always need a formula. Type in full hours as follows:

9: returns 9:00

Quick date entry:

=--TEXT(A1,"00\/00"&CHOOSE(LOG10(A1)/2,,"\/00","\/0000")), formatted as DD/MM/YY (or as you like).

112      returns 01/12/2006
113      returns 01/01/2013 (13 is not a month)
1212     returns 12/12/2006
1213     returns 01/12/2013 (see 113)
1229     returns 01/12/2029 (see 113)
1230     returns 01/12/1930 (see 113; a two-digit year returns 1930-2029)
1345     returns #VALUE! since there is no interpretation as DDMM and MMYY possible
11111    returns 01/11/2011
101111   returns 10/11/2011
1111111  returns #VALUE! because of year not within 1900 and 9999 but 111 or 1111
1121900  returns 01/12/1900
31129999 returns 31/12/9999

Using an Add-In (Ron de Bruin), you do not need the formula and the treatment.