Hi!   

Welcome to the Radium Project.   The estimate of time it takes to stake provided by the wallet is an estimate, and is not always correct. The time it takes to stake depends on how many coins you have, and how many coins other people have staking.  The current network stake weight is 1,000,454.  This means that your chance of staking a block each day is about (150/1,000,454) * 1440, or around 20%. That is about 1 block every five days. If you wanted to stake faster, you would need to get some more Radium (RADS).  This is how most all Proof-Of-Stake coins work, and it is not unique to Radium.

I hope that helps!

JJ