Reapplying Visit Visa After First Visa is approved

I had applied for the Visa for my parent recently and the Visa is approved but the Visa is not stamped in Home country yet.
The issue with this Visa is, the duration of Visa is less i.e. only 30 days. So, I am thinking of applying for Visa again after 1st of Moharram and try my luck of getting the Visa for longer duration. Will I be able to apply for Visa again without stamping the first Visa? Does any one has any experience in this regard?

when did you apply...and how long took it to get visa?

everytime we we apply we get visa for 30 days....after that we have to apply for extend it.

Visas are issued these days for 30 days. You can extend the visa for 30 days for 2 times which means they can stay here in the same visa for 90 days. They might not issue a visa if you already have a visa issued.