If this is really going to be a concern, the Reserves may not be for you. Being a Reservist is more that just your two days/month and two weeks active duty. There's a very real possibility you can be recalled to active duty for some period of time, depending on domestic and international events, or manpower needs of the CG. The whole point of the Reserves is to be available to augment the active duty folks when needed. In my 15 years in the CGR, I've been on active duty five different times outside my normal two weeks per year. The shortest period was 30 days, the longest was a year.
Be aware that by Federal law, your employer is required to give you the time off to attend IDT (i.e drills) periods and your ADT (two week active duty). This is the Uniformed Services Employment/Reemployment Rights Act, commonly known as USERRA. Look here for further... http://www.esgr.mil/USERRA/What-is-USERRA.aspx.
They don't have to give you specific military leave time, however. They may require you to use comp time, vacation, etc. I'm fortunate in that I work for the public sector and we receive 30 days of paid military leave/ fiscal year. Additionally, we receive make up pay if our leave goes beyond that 30 days. This is where L.A. County (my employer) pays the difference between my salary there and my CG salary.
As for the scenario you mentioned regarding four to five day drills vice two day drills, that's unlikely to happen in the CG. This is due to funding. The CG is a small service and receives a proportionally smaller amount of funding than the other services.