Informix 7.1 and SQL Expression

[question911]

Anyone know how to write a SQL Expression on Informix 7.1 for the following formula that I'm using to Group By?

Numbervar minextract := minute({acdgroupstats.d_time});
Stringvar amdmins;

if minextract <= 15 then amdmins := time(hour({acdgroupstats.d_time}),00,00) & "-" & time(hour({acdgroupstats.d_time}),29,00) else
if minextract >= 30 then amdmins := time(hour({acdgroupstats.d_time}),30,00) & "-" & time(hour({acdgroupstats.d_time}),59,00);

amdmins;