Right time to burst above the ground, like a tube (8)
I believe the answer is:
arterial
'like a tube' is the definition.
(like an artery)
'right time to burst above the ground' is the wordplay.
'right' becomes 'r' (common abbreviation).
'time' becomes 't' (abbreviation).
'to burst' indicates putting letters inside (inserted letters burst their way in).
'above the ground' becomes 'aerial' (ie in the sky).
'r'+'t'='rt'
'rt' placed within 'aerial' is 'ARTERIAL'.
(Other definitions for arterial that I've seen before include "Road that connects towns or cities" , "Major route with minor branches" , "Relating to major routes" , "along major roads" , "Like main way" .)