'Noon' means 'midday' or 12 o'clock during the day. 'Midnight' refers to 12 o'clock (or 0:00) during the night. When using a 12-hour clock, 12 pm typically refers to noon and 12 am means midnight.
Midday and midnight conventions There are no standards established for the meaning of 12am and 12pm. It is often said that 12am Monday is midnight on Monday morning and 12pm is midday. This puts all the times beginning with 12 and ending with am in the same one-hour block, similarly with those ending with pm.
12:00 am is always the first minute of the day, because it is always followed by 12:01 am. 12:00 pm is always the first minute after Noon, because it is always followed by 12:01 pm. Otherwise would split part of an hour between two days.
Though there is no global unanimity on the issue, most often midnight is considered the start of a new day and is associated with the hour 00:00. In the United States and Canada, digital clocks and computers commonly display 12 a.m at midnight.
Cement-Based and Premixed Grout Both are subject to variation depending on the brand and environmental conditions, but a basic recommended drying time is 72 hours when used in a shower tile job. Temperature and humidity affect the curing process, so avoid using the shower during those hours if at all possible.
Most sealers dry within 5 hours, however, there are a few that take over 2 days, which is why it is recommended to always wait 48 hours before allowing traffic to be on the safe side. If you are not sure whether the sealer has dried up, test it by sprinkling a few drops of water onto the grout line.