There is no frequent buses from Shoranur (Town which is near to Rly stn) to Guruvayoor but lot of buses are available from a placed named 'Kulappully' which about 4 Kms from SRR Rly stn. First bus is around 5AM and it will take 1.30 Hrs to Guruvayoor aprox. Better to take a Auto/Taxi or use bus from SRR to kulappully.
Other Option- Take the 56607 SRR-ERS (4.30am) passenger and get down at tcr (5.40AM) and take Guruvayoor bus from there about 30-40min run for bus.