The timechart command buckets data in time intervals depending on the selected time range2. The timechart command is similar to the chart command but it automatically groups events into time buckets based on the
_time field2. The size of the time buckets depends on the time range that you select for your search. For example, if you select Last 24 hours as your time range, Splunk will use 30-minute buckets for your timechart. If you select Last 7 days as your time range, Splunk will use 4-hour buckets for your timechart2.
Therefore, option B is correct, while options A and C are incorrect because they are not factors that affect the size of the time buckets.

Reference:https://answers.splunk.com/answers/574643/field-showing-an-additional-and-not-visible-value-1.html
To use a macro in a search, you must enclose the macro name and any arguments in single quotation marks1.
For example, 'my_macro(arg1,arg2)' is a valid way to use a macro with two arguments. You can use macros
anywhere in your search string where you would normally use a search command or expression1. Therefore,
options A and C are valid searches that use macros, while options B and D are invalid because they do not
enclose the macros in single quotation marks.

The eval command is used to create new fields or modify existing fields based on an expression2. The sort command is used to sort the results by one or more fields in ascending or descending order2. If you want to convert numeric field values to strings and also sort on those values, you should use the sort command first, then use the eval command to convert the values to strings2. This way, the sort command will use the original numeric values for sorting, rather than the converted string values which may not sort correctly. Therefore, option C is correct, while options A, B and D are incorrect.