It sounds like it should work in theory. There are a couple requirements for time intelligence to work full like marking the new table as the date table and having it include full years of dates (1/1 - 12/31).
https://learn.microsoft.com/en-us/power-bi/guidance/model-date-tables
Is there any way you can split your current date table, the one that had date + time into two, a date table with only dates and a time table with just times? I have used this technique and it works well. A time table down to the second granularity only has 86,400 rows. You create it using a time key that looks like this '00:00:01' - '23:59:59'
Then, on your data side you split the datetime columns into date and time and join it to the date table and the time table.
I will even share the SQL code for the time talbe I use:
WITH Tally ([Second]) AS
(
SELECT
ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) - 1 -- zero-based
-- Returns exactly 86400 rows (number of seconds in a day)
FROM (VALUES(0),(0),(0),(0),(0),(0)) a(n) -- 6 rows
CROSS JOIN (VALUES(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0)) b(n) -- x12 rows
CROSS JOIN (VALUES(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0)) c(n) -- x12 rows
CROSS JOIN (VALUES(0),(0),(0),(0),(0),(0),(0),(0),(0),(0)) d(n) -- x10 rows
CROSS JOIN (VALUES(0),(0),(0),(0),(0),(0),(0),(0),(0),(0)) e(n) -- x10 rows
) -- = 86,400 rows
SELECT
RIGHT('0' + CAST ([Second] / 3600 AS VARCHAR(2)),2) + ':' + RIGHT('0' + CAST ([Second] / 60 % 60 AS VARCHAR(2)),2) + ':' + RIGHT('0' + CAST ([Second] % 60 AS VARCHAR(2)),2) [Time_Key],
[Second],
[Second] / 3600 [Hour Number],
[Second] / 60 % 60 [Minute Number],
[Second] % 60 [Second Number],
FORMAT ( DATEADD(second,[second],0), 'h:mm tt') [Hour Minute AM/PM],
FORMAT ( DATEADD(second,[second],0), 'HH:mm') [Hour Minute 24],
FORMAT ( DATEADD(second,[second],0), 'h tt') [Hour AM/PM],
FORMAT ( DATEADD(second,[second],0), 'HH:00') [Hour 24],
CASE
WHEN [second] BETWEEN 0 AND 21599 THEN
'12 AM to 6 AM'
WHEN [second] BETWEEN 21600 AND 43199 THEN
'6 AM to 12 PM'
WHEN [second] BETWEEN 43200 AND 64799 THEN
'12 PM to 6 PM'
WHEN [second] BETWEEN 64800 AND 86399 THEN
'6 PM to 12 AM'
ELSE
null
END [Hourly Quartile],
CASE
WHEN [second] BETWEEN 0 AND 21599 THEN
'12 AM'
WHEN [second] BETWEEN 21600 AND 43199 THEN
'6 AM'
WHEN [second] BETWEEN 43200 AND 64799 THEN
'12 PM'
WHEN [second] BETWEEN 64800 AND 86399 THEN
'6 PM'
ELSE
null
END [Hourly Quartile Short],
CASE
WHEN [second] BETWEEN 0 AND 21599 THEN
1
WHEN [second] BETWEEN 21600 AND 43199 THEN
2
WHEN [second] BETWEEN 43200 AND 64799 THEN
3
WHEN [second] BETWEEN 64800 AND 86399 THEN
4
ELSE
99
END [Hourly_Quartile_Sort]
FROM Tally
