If you have a typo in a word, people can usually figure out what the word was supposed to be. Even if you ended up with a different valid word in the process, context lets them know something is wrong. And even if you mangle a word so severely that it's unrecognizable, the reader will recognize that there's a problem and call you on it.
Numbers are different. Every number is a valid number, so if you miss a numeral or transpose a couple or just hit the wrong key, it is not immediately obvious that anything is wrong. Sometimes you get lucky and end up with something that doesn't make sense -- a price with more than two numerals past the decimal or a phone number with only six digits -- but you can easily have an unnoticable mistake. You want to meet a friend for dinner at 7:00, but your finger slips and you type 6:00 instead.
When dealing with times, write out the words rather than using numbers. Meet your friend for dinner at seven rather than 7:00. For dates, write out the word for the month and include the day of the week as a check value. If you make plans for and type 7/14 or 8/13 when you meant to type 7/13, it'll probably be missed. If you make them for Tuesday, July 14, your friend will notice when putting it on a calendar that the 14th is a Wednesday and will ask you what day you really meant.