only below three lag formats are supported in service now

1. Days

2. Hours(should be positive duration)

3. Minutes(should be positive duration)

If your Microsoft Project has any lag formats other than above three , on importing you will see below error.

Here are some examples of Microsoft Project having invalid lag formats

Example 1( Lag which is defined in weeks is not supported)

In the below screen shot, lag format is defined in week(wk) which is not supported. so importing this microsoft project would show an error.

Example 2( Lag which is defined in negative duration is not supported)

In the below screen shot, lag format is defined in negative duration(-30) which is not supported. so importing this microsoft project would show an error.

So when you see "Only Positive Days,Hours, Minutes and negative days are allowed for lag time dependencies." error while importing, please review your MPP for any invalid lag formats and correct them and try to re-import again.