Thanks to both of you for your replies.
As suggested by ginnu, i can schedule my visa interview at the embassy using my spouse's H1 approval notice expiry date. But then the petition receipt number should be from the same H1 approval notice, right?
--------- Yes the petition expiry date has to be your spouse H1 approval notice
However, judging by what you told me, it seems i should fill in my own H4 approval receipt number and my own H4 approval expiry date so that both can tally for the visa interview.
----- your H4 Visa is based on your spouse H1 approval notice, you dont get H4 independent of H1, ( at this time you dont have H4 extension petition approved and only have H4 extension filing reciept, even if you haveH4 extension approval that will be ONLY till your spouse H1 petition) dont get confused write the H1 approval expiry date
Since i have to wait approximately 3 months for the interview, i wanted to save some time by scheduling it before i got the approval.
----------------- your H4 extension approval is NOT needed for H4 visa stamping, H4 is based on spouse H1 approval notice. you filed H4 extension so that you can be on STATUS in US it has noting to do with H4 Visa stamping from US consulate.
But since scheduling itself requires information from the approval notice, i cannot schedule before i get the H4 approval.
I would appreciate any other suggestions.
Thanks