Uptime information is not scanned in Lansweeper 4.2. This feature was added in Lansweeper 5.0, which is currently in beta. A download link and more info on the beta can be found 
here. A sample 5.0 uptime report can be seen below.
Select Top 1000000 tsysAssetTypes.AssetTypeIcon10 As icon,
  tblAssets.AssetID,
  tblAssets.AssetUnique,
  tblAssets.Domain,
  tblAssets.IPAddress As IP,
  Ceiling(tblAssets.Uptime / 60) As [Uptime(minutes)]
From tblAssets
  Inner Join tsysAssetTypes On tsysAssetTypes.AssetType = tblAssets.Assettype
Where Ceiling(tblAssets.Uptime / 60) Is Not Null
Order By Ceiling(tblAssets.Uptime / 60) Desc
To use the specified report, do the following:
• Browse to the Dashboard\Reports\Report Builder section of the web console. 
• Paste the SQL code we provided at the bottom of the page.
• Left-click somewhere in the upper section of the page so the code applies.
• Give the report a Title and hit the Save & Run Report button to save it.
• The report will now also be listed under Dashboard\Reports\All Reports.