Can Brown still hold a March 25th Election?

The simple answer is, yes. Here is the timetable from the official Commons’ Briefing Paper, together with the relevant dates.

Proclamation summoning new Parliament/dissolution of old Parliament/issue of writ
Day 0
Monday
March 1st

Receipt of writ
Day 1
Tuesday
March 2nd

Last day for publication of notice of election (4pm)
Day 3
Thursday
March 4th

Last day for delivery of nomination papers/withdrawals of candidature/ appointment of election agents [...]