What is the basic unit of time?

Hint To answer this question, we need to first explain the basic definition of a unit. Then, taking examples of the different units of time from the daily life experiences, we have to conclude the final answer.

Complete step by step answer
A unit of a quantity refers to the fixed amount of that quantity, which is used as a standard amount to measure its different amounts. For example, the reference used for measuring the length is taken as the distance travelled by the light in about $\dfrac{1}{{299792458}}th$ of a second. This amount of distance is termed as a metre.
For measuring the time, many different units have been developed so far. It is not difficult to make a list of these units of time. We all use these units of time in our daily life. For example, we call the time period of one complete rotation of the earth as one day. A combination of seven such days is termed as one week. While a combination of $365$ such days is termed as one year. We are also familiar with more superior units of time than one year, from one decade to one century.
We all have wall clocks in our homes and wrist watches in our hands. These help us in measuring small time intervals of a day. We measure the number of hours, minutes and seconds with the help of these.
But all the time units mentioned above are defined by taking one second as the base unit. We have one minute equal to $60$ seconds, one hour equal to $3600$ seconds, and likewise we obtain all the superior units in terms of one second.
Hence, the basic unit of time is second.

Note
The unit second is basically taken with respect to the caesium atom. The total time duration required for about nine billion oscillations of the caesium atom is defined to be a second. It is accepted as the fundamental unit for both the CGS and MKS or the SI system of units. This unit helps to make the observations of any experiment consistent, as it does not depend on the type of apparatus used in the experiment.