Extract time slot based on interval value - excel

Question

In cell A1 I have an interval value which is an integer which can either be 1, 5 or 15 which means 1 minute, 5 minutes or 15 minutes
In range "B1:B12", I have the sample data (it will be more)
12:03
12:03
12:06
12:06
12:09
12:11
12:14
12:15
12:15
12:16
12:31
12:32
Now in column C, I need to extract time slots based on number is available in cell A1.
If cell A1 has 15 then the column C would contain below
12:15
12:30
because first 15th minute in column starts at 12:15 then increment it by 15 mins until last available data which falls in that 15 min range.
If cell A1 has 5 then the column C would contain below
12:05
12:10
12:15
12:30
because first 5th minute starts at 12:05 then increment it by 5 mins until last available data which falls in that 15 min range.
and if cell A1 has 1 then extract everything except duplicates.
I hope I have explained the scenario properly. I am not able to think of a logic to do this in excel vba and need help with how to start so that I can try to apply the logic and comeup with a code.
Thank you
EDIT
I am adding a pic of the desired result.
if A1 contains 1 then copy all timestamps in column C without the duplicates
if A1 contains 5 then show only 5 times of 5 min interval
if A1 contains 15 then show only 3 times of 15 min interval

Answer 1

Using VBA (1) returning an array
You will need to ctrl-shif-enter
Option Explicit
Function get_unique_time_interval(ByVal interval_size As Double, ByVal input_data As Range) As Variant
interval_size = interval_size / 60# / 24#
Dim d
Set d = CreateObject("Scripting.Dictionary")
Dim r As Range
For Each r In input_data
Dim t As Double
t = Int(r.Value / interval_size) * interval_size
If Not d.exists(t) Then d.Add t, t
Next r
get_unique_time_interval = Application.WorksheetFunction.Transpose(d.keys)
End Function
(2) hard-coded outputting to C1
option explicit
Sub get_unique_time_interval_sub()
Dim interval_size As Double: interval_size = ActiveSheet.Range("a1").Value
Dim input_data As Range: Set input_data = Range(ThisWorkbook.Sheets(1).Range("b1"), ThisWorkbook.Sheets(1).Range("b1").End(xlDown))
interval_size = interval_size / 60# / 24#
Dim d
Set d = CreateObject("Scripting.Dictionary")
Dim r As Range
For Each r In input_data
Dim t As Double
t = Int(r.Value / interval_size) * interval_size
If Not d.exists(t) Then d.Add t, t
Next r
Dim v As Variant
Dim i As Long
i = 0
If Not IsEmpty(Range("c1").Value) Then Range(Range("c1"), Range("c1").End(xlDown)).ClearContents
For Each v In d.keys
ThisWorkbook.Sheets(1).Range("c1").Offset(i, 0).Value = v
i = i + 1
Next v
End Sub

Answer 2

this works as a single cell formula in C1:
=UNIQUE(INT(B1:B12/(A1/60/24))*(A1/60/24))
breaking it down:
A1/60/24
is the time interval you want (A1 in minutes so divide by 60 mins per hour and 24 hours per day to get to Excel time interval units). Then:
INT(B1:B12/(A1/60/24))
rounds you down to the start of the time period. Then:
*(A1/60/24)
converts you back up to the time of the interval in which the input time falls. Then:
UNIQUE(
pulls out the unique values.
The helpful thing here is that by including B1:B12 as a range it makes everything (helpfully) spill

Answer 3

If you accept a formula based answer then This should work for you:
A1: some inteval value.
B1:
=0.5+A1/(24*60)
Where 0.5 mean 12:00 in Excel.
In B2:
=B1+$A$1/(24*60)
And drag this formula down to where you need it.
Exampls: