Reply to an interview email

Hi guys, Just stumbled into this wonderful forum.

Today I got this email requesting an interview after I let the HR representative I was working at the time.

Hi XXX,

I hope you are well.

I tried to phone you, however I was unable to reach you.

I would like to touch base with you in regards to your application to the 2012/2013 Vacation Programme as a XXX Engineer. Are you still interested in being considered for a position? If so, I have a couple of positions available which we would like to interview you for which will be based in XXX. Therefore, we will cover your flights and accommodation during the 12 week placement.

Please let me know if you are interested and I will arrange your interview.

I look forward in hearing from you.

Kind Regards,
XXX
...............................................................................................
Here's my reply:

Hi XXXX,

Thank-you for calling today and for being so understanding of my work schedule.

I am still excited and interested in furthering my application with XXXX and the positions in XXXX sound fantastic. I have always wanted to visit XXX and the surrounding XXX region.

The earliest time I am available for contact during office hours is Friday 14 September between 10.00 am and 1.00 pm due to an all day field trip tomorrow, unless after 5.00 pm suits.

I cannot wait to discuss this opportunity with you further,


Yours sincerely,
Happy Student

Is it okay to go non formal as their initial reply isn't?