Regex - make youtube transcript lines from 2 lines to 1 line - time + text

How to replace youtube / yt transcript 2 lines into 1 line.
I have youtube transcript in text file and want to make it more readable.
Each youtube transcript is like:
- 1 line time
- 1 line text from the time
What I expect:

Before:

xxxxxxxxxx

00:20

Single line text example

00:25

Next test line

After:

xxxxxxxxxx

00:20 Single line text example

00:25 Next test line

1. Open Notepad++
2. Open find window (Ctrl + f)
3. In find window - Replace tab
4. Find what + Replace with
- Find what - this regex:

xxxxxxxxxx

(^\d+\d+:\d+\d+$)[\r\n]+(^.+?$)

- Replace with:

xxxxxxxxxx

$1 $2

5. Click Replace All button
6. Before and after
- Before:

xxxxxxxxxx

00:20

Single line text example

00:25

Next test line

- After:

xxxxxxxxxx

00:20 Single line text example

00:25 Next test line

7. NOTES:

• Tested with Notepad++
• Regex works fine with windows or linux end of line - EOF:

xxxxxxxxxx

\r\n

\n