To rebuild a index, the below query will use full to estimate the approximate time(Not accurate but it will rough estimated time either +\- 30%).
use dbname
go
SELECT IndexName = name,
IndexSizeGB = CEILING(1.0 * dpages / 128 / 1024),
ETA_Min = CEILING(1.0 * dpages / 128 / 1024) * 1.5,
LogSpaceGBRequired = CEILING(1.0 * dpages / 128 / 1024) * 2,
DataSpaceGBRequired = CEILING(1.0 * dpages / 128 / 1024)
FROM sysindexes
WHERE NAME LIKE ('indexname')
--OR NAME LIKE ('indexname')--If you
want use multiple indexes use OR condition
