Great … It is not wrong to grow watermelon in April or May …But important things to note in regard to watermelon cultivation in off season or extreme weather like hot summer when temperature goes rising beyond 37 degree Celsius is that the sprouting and growth will be seen retarded and yield will not be economical to spend on cultivation …Mulching might help in weed control and water conservation but the watermelon sown in April would come into flowering either in the middle of May or end of May which is hottest month with burning heat waves that might prevent flowering and fruit set . Even if it set fruits , it will not develop into enough size and taste and total yield of fruits in an unit area of cultivation .
To be frank , I have no idea about prevailing weather and climate in your location .You are the best judge about your location . So act accordingly and consult nearby farmers if it is worth pursuing watermelon cultivation in April