[Python] How Python Pandas perform subtraction in specific pattern of column?

There are NaN data in the Time column and has block of the data. I need to perform subtraction at specific pattern as mentioned. I tried with cumsun and diff but not able to get correct answer.

Attempted Code:

data = {'Time': {600: nan, 601: '2025-04-23 22:30:38,205', 602: '2025-04-23 22:35:08,482', 603: nan, 604: nan, 605: nan, 606: '2025-04-23 22:38:15,791', 607: '2025-04-23 22:40:15,603', 608: '2025-04-23 22:40:27,789', 609: '2025-04-23 23:40:29,255', 610: nan}, 'BatSOC': {600: nan, 601: '1', 602: '8', 603: nan, 604: nan, 605: nan, 606: '9', 607: '10', 608: '11', 609: '100', 610: nan}}

df = pd.DataFrame(data)
df['timestamp'] = pd.to_datetime(df['timestamp'])
df['time_diff_minutes'] = df['timestamp'].diff(2).dt.total_seconds() / 60


Expected output:

Perform substration in each group of availabe data at every 2nd data to previous data

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