There is only one SI unit of time and that is the second (s) but other units are often used.
60
seconds make a minute
60 minutes make an hour
24
hours make a day
7 days make a week
A solar year is the time taken for the Earth to go round the Sun, and is about 365¼ days. A calendar year must have a whole number of days so is 365 days for a common year and 366 days for a leap year. Usually every fourth year is a leap year.
A calendar month has 28 or 29 or 30 or 31 days so is not a very precise way of measuring time. Scientists and other people wanting to measure time accurately do not often use calendar months.
A lunar month is the time from the first sighting of one New Moon to the first sighting of the next and is either twenty nine or thirty days. Some religions use lunar months.
There is a very much longer
article on time and the calendar elsewhere in this web site
- to visit it please click here 
