Sorry about the late reply.
Also, I should have been more clear that this behaviour occurs in fresh nodejs version of TW5 and not in the regular import between versions. Importing between two regular files preserves the dates.
The behaviour of changing dates to imported date appears in nodejs (fresh install and importing from a regular tiddlywiki file).
The correct dates show up when importing. But after restarting the server, all the imported tiddlers show up in the current date in the 'recent' timeline. I wasn't sure if this was the intended behaviour.
The load from file command line option works correctly, the dates are preserved.
So, there isn't any problem getting the right dates even in the nodejs version, as long as the command line is used and not the import option from the sidebar.
Thanks for the response.