Mysql Problem selecting timestamp modification in last 24 hours

Hi Folks,
I have a problem with this query - all I want to do is to get the rows from a table - in this case property - that have been modified in the last 24 hours.
The query runs and looks at the prop_timestamp field, which is an auto updating timestamp field whic updated every time a record is edited BUT it just seems to ignore the timestamp comparison and just returns all rows with a status of 1 ???
I look at it an I reckon it should work but I am going round in circles

SELECT * FROM property p
LEFT JOIN property_branches pb ON pb.branch_id = p.branch_id
LEFT JOIN property_price_prefix ppp ON ppp.prefix_id = p.prefix_id
WHERE p.prop_timestamp > UNIX_TIMESTAMP(NOW()) - 86400 
AND prop_status = '1'

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