Can AS 30 be applied for interim accounts

yes, the company may apply, it is recommendatory in nature for application...

Thanks Yogesh,

Just wanted to reconfirm.. Half of the year has been passed by and now company wants to apply AS 30. Can they?

yes the company can do so,, further they have to make full disclosure as change in their A/c policies and its effects. Further the date of implementing AS 30,, For the disclosure details, you can take help of your statutory auditor or internal auditor...

what is mark to market losses

mark to market losses are recording or considering or take care of losses on change in investments with time passage. It represented as day to day change in the market.
For E.g., day to day change in particular share price. Now, you purchased that at Rs. 100/-  the very next movement it become rs. 80/-, you record the loss of Rs. 20/-.

However, this concept used in derivative market not in the share market / Capital market (difficult to calculate it).